I had my brother in laws 82 300D over in my garage last Christmas. He showed me that it was flairing so bad between shifts that it seeemed it would blow the engine.
We studied the information provided here and decided to check the vacuum line by pulling it off and plugging it. No change at all. I fiddled with the bowden cable, bu tcould not reduce the flairing. So next we pulled the cap off the modulator and pulled out the small metal flat blade there and turned it one notch counter clockwise. Saw some definate improvement. Brough the car back in and continued making adjustments one 1/8 turn counter clockwise at a time. Within an hour we had it shifting more or less correctly. It still seems to need some attention on the vacuum system, but not at least he can work through that. Before it was so far away from shifting correctly it seemed that the tranny was shot.
Read Steve Brothertons article if you have not already. He shows just what I have tried to explain here, but don't be afraid of trying this. Just make those turns incrementaly and test drive between each reset.