reverse won't engage on 1994 Mercedes-Benz SL600

All the forward gears are working fine, it won't engage in to reverse.

Asked by for the 1994 Mercedes-Benz SL600
First and foremost , check the fluid level when the car is idling and in park. If that is ok, then there is a problem with the Transmission, could even be a linkage problem, or the gear selector switch is not correctly aligned.