E320CDI Differential noise

[MBGUY]

My E320CDI Has started to make a bit of drone from the rear. I originally thought it might be a wheel bearing, but now i am wondering if it could be the differential unit.
I have been told that there are additives you can add to the oil in the differential. Does anyone know if these actually work.
The one i have been told about is made by Fortay.
A new diff costs a fortune. I could do with a cheep fix!

 

[Dieselman]

Try changing the diff oil first, you might be surprised at the difference it makes.
The oil is EP (extreme pressure) oil and when sheared down will allow the gear teeth to rub instead of slide. This is what causes the noise and wear.

You need EP80/90.

 

[MBGUY]

Good news. I had a differential oil change with forte additive. Noise is 95% Better the other 5% is probably in my head!