This could be a case of TLR-to-SLR-MF syndrome. Those TLR's with their leaf shutters give very sharp results with little effort, but MF SLRs need more attention to get the same sharpness. My first MF camera was a Yashica D that always focuses right, then I upgraded to Pentax 6x7 and got many out-of-focus shots especially the first few rolls. Now with extra effort the pentax is giving sharper results. So may be all you need is more time with the 500c until you figure it out. Or you can borrow a hassy and run a roll with it. If the results turn out to be good then you know for sure that your 500 is the culprit.