Gunk Transmedic fluid in a 1990 300sl
 

My moms '90 300SL is having problems with the automatic transmission. The reverse clutch is worn out so the gear doesnt catch sometimes. A friend recommended draining the ATF and putting gunk transmedic in and letting it run for about 100 miles. then draining and replacing. I see how this could help the transmission but I don't see this having any effect on the clutch. Am i correct here?

First, try changing the fluid and filter. Then more drastic measures.