Faulty 1960's 6 speed Meccano motor teardown

With 6 selectable gear ratios this is a versatile 3V - 12V motor. Unfortunately the 60:1 gear ratio torque is too large for the gears, resulting in a broken tooth. There is little point in replacing this without some form of clutch mechanism to to stop it happening again. The other ratios seem OK although I haven't tried stalling them.