I have a 1986 300zx coupe, automatic with 92,000 miles. I have always changed the oil at 5k miles with synthentic and the car runs great. At about 85,000 miles, I've started using a quart of oil every 500 to 700miles. I can not see it coming out the exhaust, the underneath is bone dry, the plugs do not indicate any oil fouling, compression is great, and no oil leaks are evident on my garage floor. Could I have a problem with bad valve seals? I know many Japanese engines are prone to this due to the rubber compound reacting with high detergent oils cause them to become hard and brittle and lose sealing properties. Has anyone else experienced this on Zcars?