When I first got my car almost two years ago with 174,000 miles on it, it had problems like you report with your transmission. One of the first things I did was to take it to a local MB dealer that has a shop with a good reputation, and have them look the car over to create a list of things it needed. I also asked them to see what they could do with the tranny's hard shifting.

$220 later I had a punch list and a MUCH smoother shifting tranny. I've since worked my way down the list with parts from e-Bay and OEM parts through my local, non MB but excellent, fleet oriented diesel mechanic. Maybe not as much fun as fixing stuff yourself, but I wanted to get it running as a reliable car. And, I had been told by a number of people that "the diesels always shift that way", which I knew not to be true based on riding in lot of German taxis, most of which were diesels.

Maybe that would work for you.

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rdsw
Salem, NH
1984 300SD, 260k miles and counting