I have a big problem. After I took the car for oil change, days after, my check engine oil light came on. I was thinking it was low so I took it back and they showed me where it leaked from the nylon tube out the sender. So I fix that, with new connection but same nylon to the mechanical gauge and it didn't leak but check light didn't switch off. Pressure remained good. At 2k normal engine temp, pressure was at a solid 45 psi. (25 psi at idle) Now on the highway, while driving I notice my oil pressure went to zero and stayed there till I exited highway. I can see no oil traveling through the tube. Oil level on dipstick remains good. What could my problem be, clogged oil pump screen, bad pump, bad oil sender unit? Also if pump, how hard would it be to change in the parking lot. I have jack and jack stands.