Before Christmas did a similar job on a 1979 /7 gearbox where the output shaft bearing had broken up.
After trying to find a good 2nd hand 'box decided to rebuild it.
Just a tip, try local bearing suppliers before you buy from BMW or specialist suppliers. Took all the bearings in and found that they are standard sizes. Don't bother quoting the numbers on them over the phone, these are BMW's own numbers and won't help. My local supplier even had the input shaft seal in stock, Had to order the output shaft seal but it was next day.
Total cost of bearings and seals was about £80. The bearing supplier even let us use their 60 ton press to press the new bearings on! (2nd hand 'box was around £180, no warranty).
The detent spring was replaced as a matter of course as advised by those in the know.