Windscreen wipers MK2

Hello All, I am restoring the interior of my ‘63 MK2 LHD this winter, and have removed the dash panels, so best time to fix the wipers. The wiper on the passengers side has not worked since I have owned the car. The lead collar on the wheel box spindle spins and some PO has smashed the end of the shaft to the point where it must be replaced. I have ordered a replacement from SNG, but the gear wheel is bigger and the clamp plate is different. It does not work smoothly and seems to load the motor. Anyone have any experience with this. Does anyone have a spare wheel box in good condition? Should I disassemble the rack and replace the grease? Any help would be appreciated. Thanks