FWIW, I just had the tranny replaced in my 1991 300CE @ about 175m.

The shop owner told me that the "lifetime filled" MBZ trannies that are coming in are coming in totally thrashed. It is as if the innards were sandblasted. This he attributes to leaving the fluid with the suspended friction materials swirling around in there for an extended length of time.

He recommended frequent fluid changes, doesn't have to be the fancy MBZ fluid, just the correct level Mercon.

He predicted future problems with the newer MBZ trannies because the electronic brain part now sits in the scalding oil rather than out of it.