i got the plugs out today...
no.4 is slightly rusty on the top and blackened at the spark end
no.3 was wet from oil, blackened and not so tight as the others
no.2 was blackened
no.1 was blackened and was impossible to get off as it was on so tight
http://img269.imageshack.us/i/22052010392.jpg/
http://img525.imageshack.us/i/22052010391.jpg/
but this is probably due to sustained missing from trying to fix it? its no.3 i am concerned about. i split a load of oil on the rocker cover through filling up with oil the week before, then after that run it sat for a week which is when it buggered up after 3-5 mins of warming up... maybe the oil heated up and got in there?
also the spark plugs are set to .70mm. in this post alundra shows a picture of the 'stock' plugs gap to be 1mm:
http://www.nissansilvia.co.uk/vbb/showthread.php?t=5027