Check on the suction side. I had a bunch of crud that looked like it was restricting suction. That would increase the susceptibility to draw in air from the pump shaft. You need to take off the cover and have a good look, so you'll need a new gasket and a paint scraper. Be thorough in your inspection because blockages can hide anywhere - start at the pickup and work your way forward methodically verifying that everything is clear. It picks up the oil from the bottom of the pump without a screen if I recall correctly and runs some of the output through a bypass filter, again if I recall correctly. After I cleaned the unit and replaced the seals, it seems to work just fine