Dropped the motor again today but this time had a good old look. I have found the answer!! One side of the motor bolts solidly to the frame but the otherside bolts via a pressed in fitting. On installation, tightening the mounting bolts pulls the press fitting out slightly to make a good solid connection in the frame. This is what makes the motor a bugger to move in the frame. Tapping this press fitting all the way back made reinsertion of the motor a doddle, but presumably it's now pulled out tight to the frame again. So the secret to getting the motor out easily is not tapping the motor out from above, it's undoing the bolts a couple of turns then tapping them back into the frame to push the press fitting back! Easy peasy. Or it would be if I could remember which side of the motor is rigidly attached and which is fixed via the press fittings... ?