i have the same issue on my 89 300ce,it had a delay going into reverse,one day the delay got longer and longer,to the point i have lost my reverse altogether,a mercedes specialist told me just from describing it,it sounds like the reverse piston has a hole in it,its not an easy fix,the tranny has to come out,he was telling me i need a complete overhaul for $2,000.00, i wanted to know why he couldnt just fix the reverse issue then he just hung the phone up in my face,imagine that,they think we are all loaded with money just cuz we own a mercedes-benz.im waiting on another shop thats backed up for like 1 month, he will diagnose it for free,then tell me if he can just fix the reverse,all my forward gears shift fine,the tranny fluid is brand new and smells very clean,blood red,i added lucas oil tranny conditioner and it didnt do anything.goodluck with your situation,its a real pain having to push the car and cut the wheel to get her to turn around,but if you park on a slight incline the car will roll backwards then you can shift into drive and it will be fine.

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