When you removed the pan, did you check it carefully for flatness? If it has been overtorqued, there will be a slight dimple at those bolt locations. If you then torque it to spec., the gasket is not compressed evenly. Check it carefully and it can be repaired with the usual BFH and a goog flat surface. Learned that one the hard way on my then new 1960 Corvair engine. I think they made the pan out of lead. I was really soft and no way could you get it to stop leaking except to replace it with 1961 or later. Good Luck.
PS are you using 12-16 Foot Pounds? That is the spec. in the manual.
Go to Ford and buy the gasket . Standard C4's use the same gasket and the Ford one is rubber impregnated and much tougher than a regular parts store gasket . Also DON'T use RTV on it . Make sure your pan bolt holes are not dimpled in as previously stated . Place the pan on something flat (ground/driveway,etc.) on top of a flat piece of wood and tap the dimples back out . Use the ford gasket and glue it with spray glue to the pan and then install it . Don't torque the beans out of the bolts , just nice and snug . Should stop leaking .
Wish they had a gasket like my wifes explorer 5.0's auto has . It is rubber wrapped around metal and it will not leak . You can even reuse it .