Main seal, is that the crankshaft seal in the timing cover? You may have bolts going through the block into an oil passage, the valve cover gaskets, a cracked timing cover, oil pump oring and others. First step is to clean everything very well, take for test drive and inspect for leaks, may leak immedietly or take many miles, you will see how far you need to drive to see a leak meaning you may need to clean it again and drive a shorter distance next time if bad leak. It may not be coming from the timing cover??