122S Speedo drive gear failure

Has anybody suffered repeated failure of the speedo drive gear? Car is 1964 122S, M41 overdrive gearbox fitted from new, it seems to chew up speedo drive gears in about a month - any ideas or solutions?

Are you replacing the speedo gear with another with an equal number of teeth. And where are you getting your parts from ? I bought a 1969 122s with M41 o/d and a stripped speedo gear - my problem getting it replaced is I don't know if it had 20 or 18 teeth - both of which are right for an M41, and possibly so are others - I don't know if this would make a difference to being chewed up but your speedo would certainly be even less accurate.

What color drive gear are you using. If you have a "D" style overdrive, the speedo gear should be black. If you are using the correct gear, your trouble might be with the angle drive if you are using one or I've seen were someone used a M40 internal drive which is different but interchangable with the M41 internal gear. This only applies if you are using a "D" style overdrive.