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.