I noticed your comments concerning Amsoil because I too am a big fan of their products. So here comes a little bit of a confession of what I did to my wifes C230K. When I bought the car new it was the second benz I had purchased from the same dealer, so I already knew and had an excellent relationship with one of their service advisors. Anyhow I tell him that I want to install Amsoil products throughout the car and would there be a problem with that, he said if there is don't worry about it because he would make sure whatever problem arose, if any, would be taken care of under warranty.
Well, the only reason I believed him because he had done a truck load of warranty work on my 95 E320, even stuff he would notice walking around looking under it, (he was an ex-shop foreman) while it was under the starmark warranty and even covered a few things after it expired at 100k miles. So I had no reason not to believe him. I promptly ordered a transmission dip stick so I could do the Amsoil switch-over.
I ordered the Amsoil ATF, series 2000 0W-30, and series 2000 75W-90 for the rear end. At 1k miles I installed all the Amsoil products with a new tranny filter, that's when I found out that my 2000 didn't have a drain plug on the converter. Oh well.
So anyhow I ran these products for 30k miles, at 15k miles I drained the tranny fluid and just replenished it with more Amsoil ATF, (no filter change) and of course I did 10k mile oil changes, not the 35k that Amsoil says is ok, couldn't stomach that one.
Well at 30k miles I decided to go back to the Mercedes ATF after finding out that it was in fact synthetic and "probably" better for the tranny. Or should I say the "only one that is approved for use".
When I switched back over to the Mercedes ATF at 30k miles the only difference I noted was the 1-2 shift was much harder, other than that everything else felt the same. We have over 50k miles on the car right now and I will be changing the fluid and filter at the 60k mile mark going back to Amsoil ATF because it did make a difference in the shifting and I like the Amsoil products better.
I am in no way recommending anyone else do this, I'm just relaying my own personal experiences with this topic.
Thanks all for letting me ramble!!