The shafts are pretty inexpensive - I got one from Hucky a while back for ten or twelve bucks. I don't even think they're much from the dealer.
And it wasn't the re-installing that buggered the threads, it was the removal. Someone didn't know they're not supposed to come out, and man-handled them out of there. The correct stuff is pretty cheap, so just get it done right.
Wanted: Dead, smashed, crashed or trashed gauges
BMW GAUGE REPAIRS - TACH*SPEEDO*CLOCK*VOLT METER *PODs & LIGHT BOARD*