I did mine on my 1992 300-E the workshop manual calles for 6.5 quarts with the tork converter drained and a new filter.when tighting the bolts to the pan donot over tighten it can cause the pan and gasket to warp. I used Red line transsmission fluid .
I suggest you consult your workshop manual on the correct proceeder and fluid capacity be for attemping to do this service. Buy a roll of the desposable blue towels at you auto parts store you will need them and a large capacity dain pan.
Best Regards
Bob Geco