It is not that big of an issue but if grease is used the cv joints should be periodically repacked from time to time. When removing failed front cv joints on other brands of cars. I had noticed the grease is pretty scarce on the working parts sometimes. Then again those front joints have a greater radius of actual operation compared to the back ones on 123s etc.

What does the mercedes factory manual recommend? Personally I still like heavy oil. Or at least the concept. Wear only takes place if the film of luibricant is not separating the metal parts. Whatever is used should have a good pressure rating.