I have a 93 500 SEL and the Transmission is acting up. I works perfect in all forward gears, but reverse is another story. If I put it gear and let it pull itself it will back up (not on a hill of course), but if I try to give it gas it wont move. Engine revs but the transmission slips. Any help would be awesome.

 

Assume it is an automatic transmission and I had exactly the same problem. I was told that inside the transmission a belt has worn out and repair will cost a small fortune.
It is cheaper to find a replacement transmission and install that one. Do take great care in finding the correct transmission, some salesmen will tell you that some transmissions are interchangeable, but checking with MB learned me this is not the case. Exact number of the transmission can be found on the transmission itself.
Most of the time you are required to hand in your old transmission when you buy the replacement transmission.
________
Medical Marijuana Dispensary Ventura County