I have a 2001 Toyota Camry with 433,000 miles. It is still in good shape and engine runs well. The low oil pressure light came on. I checked the oil and it was good. Manual said light may flicker on when you start and should go off as you accelerate then there probably is'nt a problem. I did that and it did. I drove 83 hwy miles and didn't remember seeing the light come on (passed through some towns I had to slow down). Came into the last town and oil pressure light came back on. Oil level is still good so I had it towed to the mechanics since the manual said not to drive. Mechanic put gauge on and the oil pressure was good (20psi) and also checked the pressure at idle and it was good. He thought it was the pressure sending unit. He changed it out and test drove it and light came back on (still good pressure when measured with a gauge). I had mentioned that the lights on my dash were out (either bulb or short in wiring) so he checked the wiring up to the dash and it all looked good. He is going to change out the sensor sending unit again on the slim chance the new unit was faulty and then the only other thing he can think of is there is something happening with the intake pan... but again we are registering good oil pressure with an actual gauge. Anyone have any ideas on what is happening?

Assuming he is correct with what he told you I would take the chance and change the oil and filter with good, name brand parts. I have seen bad oil cause this as well as a bad filter. Beyond that, the oil pump could be going bad.

My experience with these cars is that sludge has formed, which is affecting the oil light. Start using full-synthetic engine oil and a quality filter. Because of sludging issues, Toyota only uses full-synthetic engine oil in its dealerships. This should safely clean the oil galleys of sludge; otherwise, use Auto-Rx.

Have him do this while the sending unit is out. Remove the oil filter, cover with a rag, with a rubber tipped air nozzle, give short blasts of compressed air in the sending unit hole.
Deposits of whatever should come shooting out onto the rag if that's what's causing the obstruction.
Replace the oil filter and sending unit, (OE filter recommended at this point) and test drive.