A few weeks ago I replaced the rear main seal, because of an oil leak. It stopped leaking for two weeks and then it started to leak really badly again, but this time from above the oil filter as far as I can see. I replaced both of the valve cover gaskets but that didn't do it either, so I replaced the Intake manifold gasket set (including the plenum) but it keeps leaking badly. Could it be the oil pressure sensor switch? Any ideas will be greatly appreciated. Thanks