If the rear main seal leaks it will have oil on the crankshaft flange flung out onto the converter flex plate, not a little bit of oil, all of it will be on those surfaces
A gasket leak, oil pan, intake valley pan and rocker arm gaskets and rear oil galley plugs or cam plug leaks can and have made many mechanics and hot rodders change the rear main seal when it wasn't leaking
Make sure YOU know where the leak is first before starting to fixing it