If you have gas in your oil pan, then you probaby have gas in your oil. if you have gas in your oil, then you either have bad piston rings, or a bad carburetor (or injectors if the engine is newer).
The way to check if you have bad piston rings is to see if you're blowing blue smoke out of your exhaust.
the acids in the oil eats the pan over time
The fuel pump diaphragm has broken. Needs new fuel pump.
Oil spread on a pan due to a reaction with the metal of the pan. This reaction causes the oil to spread and make a coating on the pan. This helps to prevent foods from sticking.
Replace the fuel injectors and the fuel pressure regulator.
Blown headgasket
an oil pan leak is adding oil to the already polluted environment, causes you to drive with your car a bit low on oil at times, and causes unsightly stains under the car .aside from all this if you monitor the oil level and keep it where it should be , not much of anything else ,i can think of,
Over tightening the drain plug.
If your 1990 Lumina has gas in the oil pan, then there could be a stuck injector flooding the engine. There can also be a blown head gasket. Driving the vehicle can destroy the engine.
Bad fuel injector, or debris stuck in the injector not allowing it to close.
fuel pump if mechanical
For gas engine center rear of oil pan, it is a cast aluminum pan 15mm bolt and the oil filter is next to and up. When you remove the bolt oil will flow out 12+ inches back.
Could be a very rich condition such as stuck injector or float.