I'd forgotten about that!!!! Soon after I first built the Raptor back in 2002 that pin did come out and neatly cut a round hole in the gearbox housing and it was just about to fall apart . I was very lucky to get away with it and just had to replace the housing and pulley wheel. ! I have checked it and it's OK. Also, checked the belt and it has all it's teeth and it is nicely tensioned.
I can't decide if the OS is causing the snatching it's so hard to spot. The OS runs flawlessly.