did you have to shave much off the inside of the box by the way ?

from what other people have said, i was under the impression that these gearsets go straight into the F10 casings, but as you mentioned it had an electronic drive, makes me think its a post 97 box, which has a larger 1st gear.

the later boxes only have 2 extra teeth on the 1st gear (41 instead of 39). but maybe thats just enough to cause it to catch ?