Make sure that pin is there, too!!! (Part #Z260)

Also, check your (2 or 3 shoe) clutch on the engine. It might be oily, or glazed. If it slips, it will generate heat and melt your new spur very quickly.

So too will a slipping slipper. Although the slipper by definition is designed to slip, it should only do so during shock-loadings - like when landing off a jump, or hitting a big stone etc. It's not supposed to continually slip.