Oil fill plug stuck

[Mn7]

Well, we f-ed up. When we screwed the oil fill cap on last time we apparently did it way too tight. I know, I know. Hand tighten only. We missed this mark here and welcome the deserving memes. 🥴
Our best ideas to get it out have us now in a situation of a tab-less plug and some chew marks on the clutch cover. Ugh.
Before we attempt our next, least liked strategies of chiseling out a spot on the top for a flat head to screw it out or drilling just deep enough to follow with a bit to reverse it out, does anyone have suggestions to get it out?

[Vegas Street Rider]

You might want to take a dremel tool of some kind with a cutting wheel and cut a groove into half of the top enough to get a small chisel or screwdriver to bite into it. Be careful not to cut too deep or you risk getting debris into the crankcase, etc.

Tap gently. Remember going forward, let the gasket do the work to seal it. Good luck.

[Axeman88]

It's difficult, because of the rubber and plastic seals in close proximity, but I generally use heat on female threads, and try to cool the male component with application of cool water rag. This takes advantage of expansion of material with heat to increase thread clearance.

Also, I would introduce a good penetrating oil, (I use Kroil), along with some light tapping to encourage the lubricant to penetrate. WD40 is NOT penetrating oil.

If I wasn't confident about grabbing the perimeter of the cap with a pair of Channellock pliers, ( about a 10" curved jaw, or V jaw seems about right)
https://channellock.com/pliers/tongue-groove/ ,

Then I could drill the cap at two spots and use an adjustable pin spanner.
https://www.amazon.com/Trades-Adjustable-Angle-Grinder-Wrench/dp/B00V539YTE/ref=asc_df_B00V539YTE/