I've got a '97 that has started leaking oil that collects at the bottom of the flywheel housing. The oil doesn't appear to be coming down the sides of the housing, so am I correct in thinking that it's either the rear main seal or the oil pan gasket that will need to be replaced? It only leaks while the engine has been driven. If I wipe the oil off....no more drains out until after I've driven it more.