I mean I wouldn't say doing a leakdown is completely useless. You will KNOW if its the valve or the rings seeing on thats whats the test is ment to determine.... If you wanted to rebuild this motor I would def. recommend getting the head pressure tested at a local machine shop, get it decked and what not. While your there get the bottom end hot tanked and get a fresh hone for your rings and when you get it all back your looking at a few hours at most on getting it back together if your mechanically inclined and have some knowledge of doing this sorta thing. If it is your valves, please don't cheap out and only buy one exhaust valve. Do yourself a favor and do it right. You will save yourself alot of headaches in the future for doing so and your car will treat you with reliability.