My dad is on a road trip and his 4.7 liter started running rough. Pulled into dealer and drained oil to find a large amount of gas in oil. So much, made a mess when drain plug opened. Mechanic said like it was under pressure. Put new spark plugs in it and diagnostics detected bad coil. Installed new coil.

He then drove another 300 miles and runs good now but oil level seems to be creeping up again.

Any common issues here?
What should he check next?
Anyone have same experience?
Thanks for your help.

Not familiar with that car, but if an injector sticks open on a common rail, it will simply keep spraying the cylinder with gas. Not a good idea to drive it like that!

Not familiar with those either, but that can also be a sign of a faulty PCV system.

Is it under 100k? If so I believe it has a 100k powertrain warranty. Maybe let the dealer figure it out... and maybe deal with the damaged engine.

the only thing i could think is you have a dead cylinder / misfire and its gas-washing the rings.

that is the only way gas could get in the oil that i can think of, from injector to chamber (and no combustion), through rings.

What year?? All OBDII vehicles will flash the MIL when misfires occur. They normally will shut off injectors when that happens also(fuel cut)

More than likely you have an injector stuck open.
There is probably one that leaks a little after the engine is shut off and all the fuel pressure leaks down that one cylinder.
Sometimes you might notice a slight misfire at startup. It it doesn't misfire long enough for the misfire monitor to pick it up.
What I've done in the past to find those is remove the injectors from the intake leaving them in the fuel rail. Cycle the key on and off and back on a few times. That will pressurize the fuel system.
Then look at the tips on the injectors. If any are wet those are the ones leaking.