You need to go to a local paint supplier and talk to them about this.
Paint has warranties just like anything else and without knowing what kind of oil or how saturated the boards are, I can't tell you anything. Sherwin Williams is a good quality paint and their research labs have come out with some impressive products. I'd probably go there first. They may have an oil base, stain killing primer that will give you a paintable surface.
[URL="http://www.houserepairtalk.com/announcement.php?f=39&a=6"][size=3]The Ten Commandments of House Repair Talk[/size][/URL]
[URL="http://home.bellsouth.net/p/s/community.dll?ep=16&groupid=289528&ck="]Square Eye's home page[/URL]