Just remember that always what appears is not necessarilly the problem! Alloy rocker covers can leak and the oil runs down the back and drips off the filter area. I has a persistent leak that I thought was from the filter area but after pulling the engine out I could see a crack at the oil pressure switch hole. The pressure switch has a tapered thread and if over tightened it will crack that area and the oil will run down the back and appear to be comming from the oil filter area. I slightly ground the crack and JB welded it and it hasn't leaked since!