Transmission oil leak - Help needed!

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SPBenz

New Member
Joined
Dec 23, 2023
Messages
6
Location
Camberley
Car
C250
I’d appreciate your advice and help…

I’ve recently purchased a 2015 C Class Estate (W205) C250. It’s high mileage (circa 130k) but it’s generally been well maintained and broadly met all the servicing intervals.

Over the past few days I noticed a small pool of liquid behind the front passenger wheel. It looked as though it was coming from the under tray/guard pan. Although not necessarily viscous, it was iridescent.

I’ve since removed the under tray and it looks as though the fluid is coming from the automatic transmission sump gasket (photo attached).

I’ve owned the car less than a week. It was supposedly “serviced” the week before (invoice for A Service, including oil change) and MOT’d. Nothing was seen or advised. There were no previous signs of oil, if seems strange to have come on all of a sudden?

Would you agree with my assumptions? If it is the transmission sump, Is this a common/known fault? Has anyone faced this before? Is it an expensive/complicated fix? Is it the sort of thing any competent mechanic could fix, or is it recommended to get the work done at a dealer/specialist?

Thank you in advance.
 

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I’d appreciate your advice and help…

I’ve recently purchased a 2015 C Class Estate (W205) C250. It’s high mileage (circa 130k) but it’s generally been well maintained and broadly met all the servicing intervals.

Over the past few days I noticed a small pool of liquid behind the front passenger wheel. It looked as though it was coming from the under tray/guard pan. Although not necessarily viscous, it was iridescent.

I’ve since removed the under tray and it looks as though the fluid is coming from the automatic transmission sump gasket (photo attached).

I’ve owned the car less than a week. It was supposedly “serviced” the week before (invoice for A Service, including oil change) and MOT’d. Nothing was seen or advised. There were no previous signs of oil, if seems strange to have come on all of a sudden?

Would you agree with my assumptions? If it is the transmission sump, Is this a common/known fault? Has anyone faced this before? Is it an expensive/complicated fix? Is it the sort of thing any competent mechanic could fix, or is it recommended to get the work done at a dealer/specialist?

Thank you in advance.
I would MB specialist it because it will need a new transmission gasket and gearbox oil . That’s pretty much a gearbox service (just change the filter and it is ) ….maybe £250-300 ?
When was the gearbox serviced ?
Get the selling dealer to fix it under warranty
 
It is difficult to see from the photos - if anything it looks like clean engine oil but hard to tell. What colour is the fluid if you soak it up on a white tissue? Leaking transmission sump gaskets are not common and usually occur after a transmission fluid change by a "non thinking" mechanic who has overtightened the sump bolts - they are only tightened to about 6Nm from memory. The problem is that it may have distorted the sump so that may need replacing as well. If you are lucky they will have forgotten to tighten them - easy enough to check if you have the undertray off - but don't be tempted to overtighten them - that will not fix it.
I would 100% second the view to get it into a specialist who knows these cars otherwise it will end up costing you more. Ask them to fix the leak and give the car a once over if you have only just bought it.
 
btw not sure how far you are from Horndean but PCS there are highly knowledgeable and will know exactly what is needed to fix your car. Ask for Olly and mention the MB Club.
 
I would MB specialist it because it will need a new transmission gasket and gearbox oil . That’s pretty much a gearbox service (just change the filter and it is ) ….maybe £250-300 ?
When was the gearbox serviced ?
Get the selling dealer to fix it under warranty
Thank you for the advice. It’s hard to tell exactly when it last received a transmission service from the paperwork. I believe the recommended schedule is every 40k, but there is no indication it was done at the last service (127k). The previous two services were A type, basic oil and filters by the looks of things.

I purchased the car privately so I guess I’ll just have to swallow this one. Fingers crossed it’s as easy as suggested and nothing more serious.
 
It is difficult to see from the photos - if anything it looks like clean engine oil but hard to tell. What colour is the fluid if you soak it up on a white tissue? Leaking transmission sump gaskets are not common and usually occur after a transmission fluid change by a "non thinking" mechanic who has overtightened the sump bolts - they are only tightened to about 6Nm from memory. The problem is that it may have distorted the sump so that may need replacing as well. If you are lucky they will have forgotten to tighten them - easy enough to check if you have the undertray off - but don't be tempted to overtighten them - that will not fix it.
I would 100% second the view to get it into a specialist who knows these cars otherwise it will end up costing you more. Ask them to fix the leak and give the car a once over if you have only just bought it.
Thank you for the response.

The fluid is a very light (and clean) brown. It isn’t necessarily viscous and doesn’t have an odour.

I totally agree, if it is the transmission sump, it’s more concerning to have just randomly started.
 
btw not sure how far you are from Horndean but PCS there are highly knowledgeable and will know exactly what is needed to fix your car. Ask for Olly and mention the MB Club.
Thank you for the recommendation. I’ll check them out, they are about 45 minutes from me.
 
To be ATF fluid it is most likely be red or blue depending on the transmission installed . For info here is an oil leak on my car some time back , the oil was not new but as you can see it looks pretty fresh . If it were a Diesel engine it would be black , even when new.

oil leak amg.JPG
 
If it is ATF and brown, that would point to old fluid containing worn clutch pack material. Needs a full gearbox service and TC flush ASAP.
 
If it is ATF and brown, that would point to old fluid containing worn clutch pack material. Needs a full gearbox service and TC flush ASAP.
Thank you, that would make sense. Once places start opening up after Christmas, I'll get it looked at as soon as possible.
 
If the ATF is brown/black its probably too late , clutch packs are worn and will most likely only get worse. If your car has a transmission dipstick tube get a tube down there (or better still the correct dipstick) and bring a bit of ATF up on to a clean white rag/paper , have a look at it .

I did this with mine just a few weeks back and after 25+K miles it is still bright red.
 
If the ATF is brown/black its probably too late , clutch packs are worn and will most likely only get worse. If your car has a transmission dipstick tube get a tube down there (or better still the correct dipstick) and bring a bit of ATF up on to a clean white rag/paper , have a look at it .

I did this with mine just a few weeks back and after 25+K miles it is still bright red.
Too late for what?
 
I think he means too late to save the gearbox. ATF is normally a cherry red colour and if it has gone brown (or worse black) then it means that it has been contaminated by particles from inside the gearbox - which means that some wear has taken place. It does not mean that the gearbox is going to fail next week; it means that it has some wear which a properly maintained gearbox would not have; therefore it will fail at some point before a fully maintained one would. Right now you don't know if it is the ATF or not - but if it is the ATF leaking then it will most likely involve changing the fluid anyway. I've seen cars with less than 100k miles with discoloured ATF but also cars with over 300k miles with clean red ATF. I would be more concerned about sorting the leak atm. If the car has a ATF dipstick then take a look at the fluid colour on there - as already suggested.
 
Pretty much what Smiley said post #15

Too late to save the worn clutch pack(s) but certainly not the end for the transmission , It is re buildable IF the clutches have gone. The picture in my post #10 is of an ENGINE oil leak in a petrol car , this oil is thousands of miles old.

I think we are still trying to determine exactly what is leaking from your car ? ..no ?

A thing to remember is if the clutch packs are worn there must be a reason behind it . 130K miles is no reason to see worn clutch packs if the transmission has been properly serviced. If not serviced properly contaminated (old) fluid could cause a problem with the lock up solenoid action which would lead to the clutch slipping leading to premature wear.

We are getting ahead of ourselves. Let's first determine what the leak is.
 

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