Another problem I have noticed is that the shaft on the new motors is considerably wider than that of the old motors. Is there any way to change these over and just use the whole output shaft of the old motor in the new one? The gearboxes are roughly the same size, maybe I just have to take that larger shaft off of the new motor somehow and it will be the same as the old motors, is that likely?

Sorry for the vague questions, I realise they may be almost impossible to answer or even understand