1998 High Oil Consumption

My 1998 Saturn SL2 with 1.9L DOHC engine will lose a quart of oil somewhere only after about 600 miles of highway and interstate driving (55 mph or higher). However, it barely uses any oil at all between oil changes if used mostly for city driving. The car has 121,000 miles on it, there are no visible oil leaks, no smoke out of the tailpipe, or no oil in the coolant. I have replaced the PCV valve and a cracked breather hose that connects the valve cover to the air intake, and that helped reduce the oil consumption. I was thinking of removing the valve cover to see if anything was plugged, but before I do, I was looking for any other advice.