seized fill plug

The fill plug in my transfer case has been seized since I bought the truck. Now the transfer case is making a whining noise and heating up. Any ideas on how to get the plug out without damaging the transfer case or getting any metal shavings into it? (it's a 24mm plug)

tap socket on plug w hammer use air-gun

The head is pretty well rounded from my previous attempt. I tried a socket but the head of the plug just flakes away.

ive used an air chisel before carefully chisel in the off direction once it moves it will usually come right out.

I don't have air tools readily available, but I'll try a chisel and hammer this weekend. Thanks for the idea.