Thanks for the replies guys
The fact that 3 is not consistent with the rest does concern me. Now its difficult to read platinum plugs but 1,2 and 4 look like normal textbook condition IMO. They have a brown tint on the ceramic part and the firing end is dark brown to dark grey. 3 just seems too white (more so than the pic shows) and there are deposits on one side of the ceramic part.
I did a "hot" compression test and got the following:
4 cranks - approx 140,140,128,140
5 cranks - approx 150,145,130,145
Look at 3
After sticking a torch down plug hole 3, the piston crown looked more "pitted" than the rest. Also, there is a little oil in the intake pipes with a cream like residue, but some consider this to be normal on turbo'd cars providing its not excessive.
Defo not loosing any coolant and both coolant and oil look fine.
I guess oil could be leaking past the piston and finding its way onto the plug? :roll:
Maybe time for a leakdown test and some poking around with an endoscope. The thing is, the car stills pulls strong all the way upto redline, especially as I've just given her some tlc in the form of iridum plugs, fuel filter, ECU reset and optimax+octane booster.
What do you reckon. Wait until it goes or take decisive action now?