I found Bmw service centres to be the pits but independant specialists are not only cheaper but usually better too. Have you got a local independant specialist for Mercedes?
I think there is an independent one locally. Either way I will have to replace it soon as the engine is shot.
It is also true what they say about mercedes build quality.....I have had so many problems with bits falling off/out that, as much as I love the look and drive, I have lost a lot of faith in them.