The thick seal is the later edition. If you are using the old pan, you may be stuck with on old style (thin seal) pan and may have been using a new (thick seal) gasket. Bring the front seal segment of the gasket set that leaks down to your local parts supplier. The difference in seal thickness between the front pan radius and the bottom T/C cover radius is on the order of .12-.25 (that is the difference, not the thickness). Whichever seal you have, try a pan gasket set with the other one. Good Luck.