Just check whether the rebuilt driveshaft has sealed bearings. Here in Munich you do find rebuilds which are considerably cheaper than the original Beemer shafts, but without sealed bearings in the universal joints. Apparently BMW has a patent on them and does not permit rebuilds to be fitted with sealed bearings.
This means that you will have to service the shaft roughly every 5,000 kms...
Only when we pause to wonder
do we go beyond the limits of our little lives.