How do you change the gearbox fluid on a rover 216 automatic?
You need to remove the transmission oil pan. Use an oil pan to catch the old fluid that will come out. Replace the filter while the pan is off and replace the pan gasket.
Why is it that when you engage the reverse gear in an automatic MG Rover 75 1999 Model it does not move while the forward gears are functioning properly?
May I suggest that you start by draining out the automatic gearbox oil or fluid and completely refill. Even 50% might be enough, but if so it'll need doing annually to keep it refreshed. It's probably about the shear strength in the oil being reduced to the point it won't drive this very low gear any more. Years ago I had the same issue with a Granada Scorpio and the fluid change fixed it, but…