i've had similar trouble with these old porshes...usually its the old style pinion that has split..the later pinions have reinforcement at one end which helps...toothed one end...circular ridge the other...as for the axle..it could well be bent...dismantle rear axle remove wheels and roll the axle along a flat surface like a mirror or piece of glass and you'll see at a glance if its straight or not..hope that helps..these old porsches are not very fast by todayts standards..but substituting some later scalex wheels ( i use some from a from a mondeo helps bring the car closer to the track and helps running...they are also very durable