I have two blown header gaskets. I was waiting on a set of allen bolts before I replace them. I was able to replace half my spark plugs today (1,3,2 & 4) two of them looked fouled and while all four had some gas on them. Could an exhaust leak before the 02 sensor cause this?
My car isn't running super rich. I don't smell any gas at all while driving or in idle. It has a slight misfire that clears above 1500 RPM or so. I wondering if in the open loop it's been running rich due to the blown header gaskets and messing with the 02 sensor.

I will put a fuel pressure gauge on it and see. But all injectors tested at 16.5 volts.

 

Yes, an exhaust leak can allow fresh air into the pipe and the O2 sensor will interpret that as too much oxygen present in the exhaust. The engine ECM will try to add more fuel to burn that oxygen, but in reality the engine is being over fueled and fouls the spark plugs.

 

Yes, and BLM's will be reported as lean, especially on decel.