My 1992 244 with 143,000 miles on it, has an oil leak coming from the rear of the head, close to the firewall, and slightly on the passenger side. There isn't any oil above where the head meets the block. It leaves a puddle about two inches in diameter when it is parked over night. I replaced the valve cover gasket (torqued to specs)last week-end, hoping to get lucky, but it hasn't helped. I changed the oil and inspected for coolant contamination, but it looked ok. (to the naked eye). Is it possible that the head gasket is leaking oil externally with no internal signs or coolant mixing?
If I replace the head gasket, do I need to send this head out or is it acceptable to just check it for warpage with a straight edge and a feeler guage? I have heard that the 2.3 head rarely needs machined.
I am not new to building engines, but are there any tricks that I should know about replacing the head gasket in the Volvo?
Lastly, due to my constant need to improve the performance of all the vehicles that I own, does anyone have experience with an aftermarket cam shaft that would be worth upgrading to while I'm in there?

Thanks Very Much!