i looked into rebuild options and finally decided that new was the best choice. no rebuild will be as good as new, since they can't use the same high quality joints bmw uses. they all drill out and retrofit to inferior snap in joints or spot welded joints.
so it came down to about 400$ for an inferior rebuild + 100$ for a guibo and CSB.
i went with a brand new driveshaft from tischer, ~550$ (+shipping, tax, etc) but this includes a brand new BMW guibo and CSB and completely rust free. rebuild made no sense.