The modulator affects shifting firmness. Slipping while in gear is due to wear, problems in the valve body, incorrect fluid level or type, or a worn pump causing low operating pressure.

Check the fluid level before getting carried away. If it's been >30K miles since the last transmission oil and filter change, the time is well past and could be a contributing factor.

__________________
Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]