Replaced the fuel pump on an '00 Lesabre (about time GM gave us an access panel in the trunk so tank doesn't have to come down). After the replacement fuel leaks from around O-Ring. Therefore, I've taken it back out 3-4 times, using different O-rings..... the one that came out of it was flat-round, and the one that came with new pump was round-round. Now I've tried a different round-round one....and the old flat round one....but I cannot find another flat-round one anywhere---- parts store; dealership; or junk yard. Still can't get the leak to stop...... what now? Doing something wrong Or what? Should I try some sort of Permatex in addition to the gasket?

Double check, there may be 2 O rings in there side by side. Put a little lube on before you slide it on.

Only one gasket on the old pump. This is frustrating me, as I just can't fiqure why it'* leaking....it seems to be quite tight when buttoned up...but fuel still seeps from around the ring area.

Was there much corrosion around the ring? I would look at how the ring sits, in must me on a flat and clean surface. Also check that the metal ring is not bent, might be worth going to the dealer and purchasing a new metal ring. finally, the larger the rubber ring the better for your situation. Consider buying all the rubber rings at Rock Auto, compare them, and install the biggest one that will fit.

The only other thing I can thing of is that maybe the metal ring is not being turned all the way to the close position. It often takes a chisel and rubber mallet to get the metal ring fully in place.

I cleaned flange really well, and did get another metal ring.....the O-Ring is the "G-27" AC Delco part....which is a flat round seal (not the "round-round" seal that was sent with the replacement pump)......Now....as I got to thinking about how I installed it--- I put the rubber seal down, then put the pump in. Is it possible that the pump should go in first and then the seal? What I did was put a bead of permatex around the flange, put the seal down over that, then put the pump in. It seems to be holding now....but if the seal is supposed to go on last before putting turning the metal ring on will this cause a problem?