P229 jamming/ejection issue

I recently acquired a p229 made in 2008. There was only one previous owner and he said he had shot less than 800 rounds through it. I shot the pistol for the first time one day before my ccw class with no problems, and really liked it. At the qualification for ccw, the pistol jammed (did not eject spent cartridge) twice. I wanted to get back in the range after the class to see what was going on with the pistol, but the range closed before the class was over. Today I got out and ran some different ammo (MagSafe) through it that I got at the range. The same thing kept happening. I tried loading the mags half full, full, loaded with federal, loaded with MagSafe... It did not seem to matter. The pistol was clean and lubricated, although I only used oil on the slide/rails and have been reading that I should use grease. Is it possible that grease (or the lack of) is causing this?! I am also wondering if sig made a heavier aftermarket spring for the 229 that could help the slide slam shut. I put a spent shell in the barrel and pulled the slide back 1/3 and released it, and it wouldn't grab the shell. When I pulled the slide back all the way and released it, it grabbed the shell and ejected it when I pulled the slide back again. I looked at the extractor, and it looks ok.