Engine light on, misfire, knocking

Well, I've sussed out what it is. Whoever put the spark plugs in last time may have cross-threaded no.6 (I'm presuming it's no.6 - the 2nd one from the front of the right side of the right bank looking from the front of the car, next to the oil filler). I took the coil pack off, looked down the recess and it was rather black and sooty compared with it's neighbour.

I tried a couple of deep sockets on it at first, either they spun it or they didn't fit, but anyway, I got the long-nose plyers on the electrode tip and sure enough, lifted the spark plug straight out - no threads in the recess.

This means it will need helicoiling, but does that mean head off or can it be done in-situ? What happens with the spark plugs then, do I have to buy one odd one every time or do they insert a sleeve and thread it? I've never seen helicoiling done before so not sure of the procedure.

I'm a little happier now I've seen what's wrong, put my mind at rest a little.