Right then.
Had a gander at the insides of the bores today. The pistons look okay, though very black. All valves were a manky rusty colour, but no obvious damage, with the only slight bit of pitting to #2 cylinder though it didn't look like it had been done anytime recently.
There were a few very faint vertical scratches in cylinders 4, 5 and 6 but not so much that they were instantly noticeable.
The problem, it would seem, is cylinder #2. Much as I wished he wasn't, Chris was correct in that something has passed through recently. There are 2 deepish scratches (deep enough to snag a fingernail, for example) 1 of which I managed to get a crap picture of (below). It would also appear that something has twatted the spark plug as there is scratching to the edges of it. Though that may just be my hamfisted removal of them
So, will 2 scratches (1 reaches about 1/3 of the way up the bore, the other about 1/4 way up, from roughly BDC) mean a head-off and costly engine work? Or can I get away with sticking the turbos on and turning to prayer?
Piccies:
General state of my spark plugs (Denso Iridium IK20's)
#2 spark plug top:
dodgy photo of the scratch to bore #2 (runs about 10 degrees from horizontal in the picture - didn't bother rotating it!)
:edit: Also noticed a fair bit of black oil around the head gasket area inside the bore - is this normal?