I once had gas leaking into the oil pan when the diaphram of my mechanical fuel pump had a hole in it. The truck still ran normally. I don't know if this engine has a mechanical pump, but if it does, you might check this out.
Gas out the tail pipe should be viewed as a symptom of the same problem that is causing gas in your oil sump. Doing so would probably rule out the above solution and get you looking at the internal engine parts. A burned exhaust valve and a hole in the piston would cause both symptoms. Too lean a mixture could cause both holes.
Check your compression ratios, or just turn the engine over by hand and when approaching Top Dead Center on each cylinder, you might feel one which turns much easier than the others. If so, that is the offender. Good luck.