The owner's manual doesn't list any recommendations on changing the rear differential fluid on the rear drive C class.
The dealer has recommended it the last couple times I have been in but I have deferred.
Couple of questions:
How often, if ever, do you guys change your differential fluid on your non 4Matics?
Does the OEM plug have a magnet? If not, I will buy a Dimple brand plug before I do it.
http://www.drainplugmagnets.com/mercedesbenz.php (bottom of page)
In general, will the dealer use an aftermarket plug if I decide to ask them to perform the change?

 

I change mine every year along with the tranny fluid. Doesn't cost much for this piece of mind. I run Fuchs 4134 for the tranny and castrol 75w90 before but Fuchs diff oil now. We reuse the hardware for the rear diff after cleaning it.

 

^^^ Agreed. I use Mobile 1 but all the fore mentioned fluids are good.

 

Every year? Wow, that seems like a little bit of overkill...but since MB doesn't give guidance, I suppose it's whatever makes you comfortable.

Does Glyn or any of our other genius gearheads have any input?

At least, does anyone know if the OEM plug has a magnet?

 

I go more off mileage than time. I caught the mention of changing it with the tranny fluid which I do as well, but missed the 'every year' part. Every 30k or so is comfortable for me. Keeping in mind these are synthetic fluids. This may help...

 

I do mine every 60k miles with Redline. Much better than the lifetime interval that my user manual seems to imply.

 

How much fluid is supposed to be used? (non-4matic)

 

1.1 litres.

 

Called and spoke to SA. He said every 4 years or 40,000 miles. Look under rear axel in manual.

They are quoting $299 American Dollars.