There was a post somewhere where someone said one of his cam tower bolts was too long, it had been put in by the PO and when tightened down had broken through the bottom of the hole into atmosphere causing leaking there, he ended up putting a stud in there with sealer, this could be something to look at also, if you can't get a stud at least put some sealer on the bolt, I would check all four next time you're in there to make sure none have the floor broken through with or without longer bolts.