I've located a nice 50/5 at what I feel is a reasonable price. I've read lots of opinions about it being underpowered, but that doesn't really concern me. It suits my riding style and the routes that I prefer to take. What does concern me is that somewhere along the way I've read about a parts availability issue related specifically to the 50, not the 60 or 75. I think it was related to pistons/rings. Any truth to that? Should I keep looking until a 60 or 75 comes along, based solely on a concern for finding parts when needed?