1995 s500 oil pressure fluctuations
 

95 s500 119 v8 87,600 miles, lifters made noise ,changed all plastic overhd pan head assembly, had 2 cracked ones, engine ok for appx. 2k miles lifter noise back plus oil guage pressure variables. pulled pan and checked strainer, no restrictions, inspected oil pump and removed spring./ stretched spring slightly and fired up, no noise better oil pressure reading for 2 days. problem is at idle getting 1lb. 1500 rpm= 2.5 over that pressure reads 2.8 to 3. cold engine =1.5 lbs =1 at idle. cannot find new spring for oil pump. is problem oil pump or pressure relief spring etc. mechanic and i are baffled, any suggestions/ on best course of action? car is otherwise perfect and oil 20w/50 changed every 4k thank you