1996 merc grand marquis coolant in cylinder 8?

I own a 1996 merc grand marquis 4.6 vin w. my engine light came on and had a cylinder 8 misfire wich i could feel in the engine it was. i pulled cyl 8 plug and the plug was wet with coolant. i thought right away headgasket but the plug boot was also dripping coolant. so if the plug boot was wet with coolant as well maybe its not the headgasket. how would the plug boot get wet when the plug was still tight in the engine??? any ideas?