[heas1]

HI
wasn't cheap but we seem to have resolved this issue,
I took the van into another mechanic and he read a misfire on pot 5 so he did a water pressure test and in his words when he'cranked the pressure right up, the cylinder was letting in water' hence the fouling and mis-fire.
he replaced the spider advising me that one of the sealing rings was letting by and so far, so good the mis-fire has stopped.