cylinder # 2 keeps fouling out plug on 5.4 triton V8 on 1997 Ford Expedition

Tried gunk head gasket sealer/repair and waited a few days and put new plug in....still fouling out plug...Expedition has 205,000 plus miles on it so I am guessing it is a head gasket?.... what can I expect a shop to charge me for repair and what all should I have done while they are doing it?

Asked by for the 1997 Ford Expedition
Im thinking its bad or cracked rings on that cyl , no or r u thinking
No compression on that cyl??