Oil usage in 3.1 V6

My daughters 1992 Lumina has a 3.1 V6 and has started to use a lot of oil in the last 4 months. You can smell oil in the exhaust but it does not smoke. It uses about a quart of oil every 500 miles but seems to run well. We changed the plugs recently and they were very dirty but we hadn't changed them for about 45,000 miles. The compression is fair ranging from 120 to 180 psi in each cylander. The cylander that had the best compression had the worst plug. The engine does leak but it does not leave spots on the driveway. Has anyone else experienced this and been able to resolve it?

Thanks,
Dave

did you get the right spark plugs and gap them to spec...?

I did a double check and the correct plug and gap was used. Is it possible that the valve guides and seals are worn so severely that it would cause this massive oil usage?