I had problems with my start motor, so I ordered a new back plate with the brushes at Stein Dinse in Germany (about 35 euro)
and mounted them without problems, but when I tryed , the start motor reved hard but the engine dint't cranck over,
afther looking, the back plate was in an wrong position : on the house of the motor (where the magnets are,) there is one little mark a little bit higher (if you look good) and on the back plate there is one of the many square 'hole' where it is supposed to match, instead of the larger cut away of where one of the mounting bolts are supposed to be.
so maybe a good idea to mark the whole things instead of having a lot more fun like I did

P750 FAQs p.2