97 Cavalier Oil Leak

Help, I have a 1997 Cavalier OVC 2.4 engine that has just developed a severe oil leak. I have replaced the crankshaft seal with no effect. I cleaned the underneath off and let it run for about 15 minutes and there was no leak. When I ran the vehicle it developed the leaks again. It appears to be leaking on the upper side/ passenger side but I can't see what it could be. The oil pan is not leaking. Any suggestions would be greatly appreciated. Thanks

I had a decent size leak that a shop told me that it was the oil pan. They were wrong! I noticed oil towards the top of my engine so I replace the valve cover gasket. Sure enough, the problem was solved. Is the top of your engine oil free? I was not losing enough to notice a loss of oil per the dipstick, but it sure left a spot everywhere I parked.