I have a 32 coupe with a SBC 327 that was put together in 1995. Last couple of seasons it seems our oil pressure is going south. At start-up it is around 35-40 but after heat up at idle it is close to 0 maybe 4 to 6 running down the road it sits at about 20. Engine runs fine and has no valve clatter. We take car on a couple trips a year and has about 22,000 miles. I am concerned about Louisville this year with this pressure. Does this engine need to come out and be redone or what suggestions are out there. Is this common? I have run 20/50 castrol and just tried 15/50 mobil 1 same results.