Hi Pluggers,
Not wishing to steal your thunder, I've cut and paste mast replacement instructions taken from an american web-site. Unfortunately no piccys so I'll be interested in your posted instructions with views.
Mast replacement, both OEM Hirshman units.
One (toothed) was balky despite oiling often didn't retract fully, other (smooth) had a broken nylon actuator and didn't go up.
If your actuator motor/mechanism is working correctly, replacement process is straightforward if nylon actuator is intact (5 minutes), and if broken inside the antenna mechanism, it's only a few additional steps to repair it (maybe 30 minutes).
When antenna is down (radio off), unscrew the antenna retaining nut and turn on radio - now quickly, as antenna extends, keep pulling on it until the antenna and all of internal nylon actuator pulls free from antenna motor mechanism.
Note the way the plastic tooth drive is. Smooth side is pointing toward the rear of the car and the geared side is pointing toward the front. Best practice is to take the old one to the supplier when ordering the new so as to get the correct mast.
If the broken actuator has part of it inside the actuator motor mechanism, you'll have to remove the motor/actuator from inside the boot and disassemble the unit to get to the remaining pieces(s).
To get to the actuator motor pull back the moulded carpet in the boot and remove a handful of screws and the top retaining nut inside the boot. Disconnect power/control cable, to remove from car and open up the antenna mechanism case and remove actuator piece(s). This is also a good time to lube the internal gears etc.
Installing new shafts - once old antenna shaft has been removed, turn off the radio (assuming it was on, otherwise turn it on wait a few moments for it to “extend” then turn it off… ) and quickly insert the end of the new antenna mast nylon actuator down into the antenna mechanism opening and let the mechanism pull the actuator down into the automatic antenna unit. I wiped the extended shafts with a light machine oil and plan to keep them clean to avoid future malfunctions.
Now enjoy your new correctly operating automatic antenna on your Mercedes.
My own mast is just beginning to stick so I'll have to do some work on it in due course.
But what got me was, I asked about discount because my car is 10yrs this year and was laughed at and told im lucky to be paying £20 for the mast and not £80-£90 for the newer cars 
dont newer cars have them built in to the rear window?But am I right in thinking that I should get a discount or am I going mad?Cheers for any info.
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