how can I replace oil seal on belle electric 150 minnimix gear box?

over loaded my belle 240 volt, 150 minnimix. When I started it pushed the worm gear out of the gear box forcing the bearing, blue oil seal, and circlip, out of the gear box housing.I have tried to refit it but cannot get the bearing to seat back into its recess, stopping the oil seal from going back in completely thereby preventing me from getting the circlip back in position. When I have tried to refit the worm gear by winding it in with the drum it seems to pull the worm gear in, but the bearing seems to move back along the shaft by about 5mm preventing me from getting the circlip in.