ive had a funky 500 trans or two,,another 550 improvement was the way the end float on the shift drum was held in check,,the 500 also lets the drum slip side ways so the fork goes with it and the gear dosent fully bite then,it just makes it worse,a well cared for trans will hold up ok but once they get shifted too fast or flat shifted the trouble starts,,it only takes several good high load jump outs to bend and wear the fork aswell as damage the dog/slots/.i dont have a 500 now only 550,in a 500 frame/badges etc.,i stocked up on 550 engines and transmissions.