zc oil pressure

has anyone had problems with used japan motors and keeping constant oil pressure. mine was real dirty when i got it and i took pick up tube off and cleaned it and it seemed fine. then it sat for a while and i went to drive it again and after an hour the pressure went back down. so i went back to shop put guage on it and it was aobur 15 to 20 psi. i shut it off and restarted bout 5 minutes later still at operating temp. and it was fine 20 to 25 at idle and 60 when on throttle. i think i am just getting cramp clogged in pick up tube or passages is there any good way to clean it and keep it clean. also pick up tube gasket tore when i took it off last time so i cleaned it all off and used some gasket maker, wondering if that might not be working and possiblilty of sucking air in through there instead of oil from pan?? any ideas or advice let me know i havent' got to tear into it yet, but i have a new pick up tube gasket on the way from honda so that going in for sure.