Given a sufficient amount of time(hours, not days), a GOOD engine man could narrow your problem down to a specific area, much narrower than "seals or pistons". Granted, it very well could be that something has failed catastrophically, and taken other components or cylinders with it, but you can be sure that if somebody has to "take it down" on YOUR nickel, he is going to sell you a total engine rebuild, which you may or may not need. He will tell you: "Once we've got 'er down this far, ya might as well..." We take our race engines apart like that, but NEVER a customer's! IMHO, you need to proceed with caution, and ditch Mr. Sealsor Pistons. Mark