My gripe is that they don't hold up as well as the rest of the car, or if it fits better they don't tolerate neglect as well. I can go buy a ragged out 80's Volvo and the last thing I'm worried about is the trans, it's the first thing on a Mercedes.
I'm sure they were fine new and I'm sure if they are expertly maintained they are in keeping with the rest of the car, but while it's pretty easy and cheap to catch up on some worn suspension and brake work and do some odd and end fixing on a Mercedes engine, a trans is a lot of work for a DIY'er not to mention overly expensive to replace. It's kind of a drag for guys like me that buy cheap old cars as hoppy/drivers, and honestly it's sort of put me off Mercedes in general after a half dozen of them over the years all exhibiting the same wear regardless of the condition of the car they were in.
I still have one but only because it was a really good deal and it had been awhile, it has 180K on it, the engine and suspension are original and great, and the trans is slow into reverse and can't be adjusted to shift 2-3 quite right though it isn't flaring(yet). It's had fluid changes and such, just a pretty typical mediocre old Mercedes trans in an otherwise great car. When it craps out the car will go away.

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One more Radar Lover gone...
1982 VW Caddy diesel 406K 1.9L AAZ
1994 E320 195K