Im no transmission expert but cured my 94 E320 of slipping (mostly in reverse gear) by adding blue devil stop leak. Now this was a barn beauty..the car had been sitting and full of mice with low trans fluid levels..not being driven. (owner lost her license) and it had issues from sitting..I added and changed fluid and fooled around with additives and eventually its 100%. (also changed the Vacuum modulator valve, which began leaking and created a huge smoke issue!) Now 200K miles and going great.

Good luck Dave..