My 96 GM has started using oilin the past 10-15,000 miles. It has 190,000 miles now. Probably a quart every 2,000 miles. I know some will say that's normal useage but it never used oil in past so why would it start using it. No oil leaks. Checked pcv valve and it was fine. I do normally use synthetic and lately has been 5w30 Castrol Edge but I use whatever is in stash. Any thoughts on why the sudden use of oil that did not exist in past.