I'm kinda not up to date on nailers............but, are you using the right nails? And......this is far fetched, I know - but, with guns....well, let me put it this way. I bought a brand new S & W 22-A handgun. Took it home, fired it using remington .22's. It kept having ejection problems. I was kinda ticked, till I did some reading. Turned out that particular gun just doesn't get along with many of the ammo brands, for some reason.
I bought Federal .22's, and have fired probably 1000 to 1500 rounds through it with no problems.
Just a thought, as far fetched as it is. And, since you said you oiled it.....(in line oil?)