what i did to remove the worm drive from the motor was this........
get a pair of pliers and grasp worm drive. with the wire cutter part then get a vice and open it till the motor fits inside and the pliers rest on top ,and then hit the centre of the motor where the worm drive is with a thin nail this will push the motor out , to put the new one on , i used a small socket to gently tap the new one back on .
would have been so much easier to explain that with pictures