Dave Stop! This exact thing happened on my VX220 on the same plug (as i assume your engine is the opposite way round to mine)
I have a new cylinder head now BUT i put K-Seal in the old one and it withstood 7K miles of abuse and didnt even look close to letting go (Track day included and the VX220's engine bay is more hostile). Spoke to a chap at K-Seal and they use it in motorsport and cured a K-Series Elise S2 with Head Gasket Failure!!
I put one bottle in, warmed the engine up and it stopped in literally 5 mins. Engine was fantastic ever since!! Im not affiliated with K-Seal id like to add, i just wanna let people know its bloody great and could save you lots of money!!