Oil leaks are sometimes hard to locate. But a good, thorough engine cleaning is a must to help isolate the source of the leak.
Any seal or gasket can leak a lot if it is excessively worn or the bolts are loose. Don't over tighten the valve cover bolts. They break easily.
From the last part of your posting, I would suspect the oil pressure sending unit is leaking. The oil light does not report oil level, it reports oil pressure. Of course, if the level is low enough, pressure will be zero.
Take the car to a Chevrolet Dealer and ask them to check the oil pressure sending unit, rear main seal, oil filter, oil pan drain plug and valve cover gaskets. If the motor has a lot of oil pressure there is a race-car trick when replacing the rear main seal.
Spray engine w/ de=greaser, and wipe/rinse clean. Make sure oil is full, and start car, looking at valve cover gaskets, oil sender, oil filter and housing, etc.
If you know that the valve cover gasket is leaking, replace it and see if that stops the leak. If it doesn't, then at least you have taken that out of the equation.
Look near the oil drain bolt and make sure it is tight. And check the oil pan. And check oil filter. And check the motor it maybe cracked
What about LIM gaskets, will they leak oil?
1995 firebird w/3.4L, 88000 original miles. I bought the car recently and found a puddle of oil the very next day. Took it to a shop and they told me I had a rear main seal leak. Charged me 800. plus fluids and seal. Called me when they were done and told me it is still leaking but not from the rear main seal. Suggested that in order to fix leak guaranteed would require removal of engine and put new seals everywhere for additional cost of 1500... Since then I have tracked how much oil it leaks per miles. It seems to lose 1qt per 250 miles or a lil less miles. The leak is only when car is running and for a few minutes after it is shut off.. It is coming down the back between tranny and engine. The guy who did rear main seal says it is impossible for seal to still be leaking and he "thinks" it is camshaft leak. I personally see the passenger side valve cover is leaking, but can it leak that much? (and there is not oil on the side of the engine where the leaking valve cover is.) The engine is pretty much clean except the back of it and around the valve cover. I did notice that sometimes the low oil light is on when 1st starting car and remains on until second start and additional starts even when the oil is full and I wonder if it can be leaking onto switch?
