Well here is a thing, comments please ...

After altering the gap, no diference.

So decided to lengthen the wastegate rod to lessen the boost, now running (as per boost gauge, not sure how accurate they are!) 13-15PSI. It was running at 16-17PSI and had been for about 10k miles, with not a pick of bother.

Now it hiccups a small fraction that it used to. Still trying to get some replacement plugs! I wonder if the C59C are just a nuisance at the mo.

Cheers
G