I find the characteristics of your PY10 puzzling. I also have a PY10 (1977) that has some flex in the bottom bracket and one of the most forgiving rides of any of my other French or Italian bikes. I can tell yours is the next generation as it sports the newer (back then anyway) graphics, single pivot brake mounts and what appears to be possibly shorter rear chain stays. I notice not much space between the down tube and rear tire. My bike appears to have a bit more space. I also wonder if at some time in your PY's life someone didn't fill the tubes with foam. That was a idea back in the early eighties trying to stiffen frames. Not sure if the foam ever worked out but could be worth a look.
