Fuel pressure regulator leaked once

1997 3100 Cutlass
Smelled raw fuel. Shut car down. Popped hood. FPR was wet with fuel on outside. By the time I found a light to investigate, the fuel was dry and I can't get it to leak again. I pulled the vac line to check and no leak there - engine running. Should I replace the FPR, or just the o-ring/gasket? How can it leak once?

Welcome to AF, get a pressure gage on the rail check for pressure leak down after shutting off, should drop very slowly, either way I'd replace the seal and the reg, dangerous condition any fuel leak.