Please help! The only way I can get the tranny into reverse, is to do so while the car is rolling either forwards or backwards, with the clutch in. All forward gears work fine.
Thankyou in advance for any replies.

 

Have you tried checking the transmission fluid. I had a similar problem with a brand new c230 recently. The car was shipped 2 quarts low on transmission fluid. The car would drive fine except on a certain road. The fluid would be unlevel at this time and cause the car from not shifting properly.

 

Keep the clutch in, then shift to 1st before shifting to reverse.

 

might need your clutch cable adjusted as well