did the B&O tech tell you what the problem was ?
it is fairly easy to change the 45rpm trimmer on the main board (something he has done I presume) but there could also be an additional problem from the pitch adjustment pot, something that you probably tried to adjust....that is just if the speed is too slow/fast ?
if your complaint is about speed fluctuations then its more involving for the untrained ?! Caps and or transistor problem ?!
if you would be in Perth I could do it for you, but.....
beolover blogs are a good address to study !!
best of luck