1988 Lesabre oil disappearing??? Of course not, but what?

Sometimes small leaks are very hard to see, but they will account for substantial oil losses. This could be below the engine, such as oil pan loose or gasket damaged, front crank seal leaking, rear main seal leaking, etc. Dripping valve cover gaskets can also account for a lot of oil, and you may not see it unless you intentionally look for it.

If you are actually burning oil, a catalytic converter which is functioning well can hide some of the blue smoke which used to clearly identify an 'oil burner'. The converter will, however, soon be inactivated if large quantities of oil are fed to it.

That age of car.....I wouldn't spend too much time trying to fix that kind of oil consumption. Just make sure you aren't overfilling the engine oil. 1500 miles for a quart isn't really that bad, you should see what the Northstars gobble up.

Ian