If like my earlier 1984 & 85 300D, if the Bowden cable adjustment is too loose it will shift high. That happens when the plastic adjuster cracks and falls apart. Wonder why such high-end masterpieces couldn't have used metal adjusters. I don't think the plastic could be easily replaced. I just cut & slotted 1/4" fuel tubing to set the position and has worked fine for years. Main thing is to drive it and judge if just "shifting high" or if it is flaring between gears. As mentioned, that could be worn clutch plates (my 96 Plymouth van, since fixed) or sometimes an easier fix in these M-B trannys (post 2).

I think Jake is realistic on pricing. If parts weren't so expensive and/or unobtanium, these cars would be more valuable. Re "crappy Jap cars", read the book "Into the Wild" and see how the Park Rangers found the kid's old Datsun, which his dad had berated, and drove it long after dad's Cadillac was junk. Anyway, you M-B guys are mostly tolerable, at least compared to Tesla fanboys.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans