What would cause the right rear tailight not to work. the other lights work fine

Most likely just a bad bulb or poor electrical connection at the bulb holder. Look at the bulb see if the bulb filament is broken or the bulb looks discolored or perhaps water is entering the lamp causing the bulb to fail prematurely. Check for power to the bulb. You would have to use a "12 volt test light" or preferably a volt meter.

I've had this problem and resolve it by turning the lamp a couple times. The connection seems to oxidize. I have been doing this on my '95 for 5 years every once in a while.

Check the bulb assembly in your backlight might be failing. Mine did this and after reaplcing the assembly ($80) the tailight worked fine. This is a common problem with BMWs.