I forgot to mention another place to check-when was the last time the gasket on the oil filler cap was replaced. You can lose a lot of oil through the cap to the top of the engine and not even know it, also it can let air into the system and pull more out via the flame trap. Does the top of the engine have alot of oil stains on it. Try to find out just where the oil is weeping out from. The large freeze plug looking thing ,half way on top of the block can let oil through and then boil off and make it seem your losing more than you really are. I sealed mine with jb weld and stopped that leak. Just pointing at a few places-another is the small 7mm bolts holding down the valve cover,if oil is leaking around them in certain places you can take them out and wrap them in teflon tape and reinstall-that will stop leaks as well.
Hope that helps
Poolman