There is an oil leak from right side of engine. oil has gotten really low yesterday but oil pressure light didn't come on. I also noticed that oil only seems to be leaking when car is running. I checked the valve cover gasket, oil pan gasket and bolt, and oil filter and they are all good. There is oil on the water pump/ps pulleys and belt but not alternator/ac belt. no blue smoke from exhaust either. I recently changed the oil and replaced the oil pan gasket. Still leaking. My question is what is causing this and a rough estimate of the parts needed to fix the problem?