I just did a similar thing on my 1987 Porsche 928S4 tranny. Its a MB 4 speed unit as well. I had a 2-3 flare and the springs seemed to cure it under lighter loads...its non existant now.

however when i put my foot to the floor i still get the slip/flare...rpms increase rapidily between the shift, then it grabs
I think i have clutch packs that are going.
157k miles and 450rwhp 424 rwtq now.