I recently purchased a 1980 289ZX with 30000 mi. The oil pressure was slow to show on the gauge and showed only about 30 psi when warm. I was told that a Nissan dealer had checked the car out and determined that the gauge was defective and not to worry about it. Not having been born yesterday, I pulled the oil pan and the pickup was completely clogged with what looked like flakes of plastic. It wouldn't dissolve in paint thinner. My guess is that the PCV or crankcase vent hose was disintegrating on the inside. I cleaned the pickup and wiped out the oilpan and immediately got instant pressure and about 60 psi warm. I passed this on to a couple of my friends and one found the same problem. The pan can be lowered enough in the car to remove and clean the pickup without lifting the engine. Hope this helps.