Well this time I was determined to do it myself. I've been running SVO and as per advice pssssssssssssssss drip drip drip.... So I got the cheap o ring kit (will get Viton later) and after dismantling the bits that needed moving I finally swapped out the top one, easy enough. 9/32 fitted my security bolt better than the 7mm as I've read. I thought I'd scored the FIP body in the right place - looked good to me. Ooops. Nope wrong bit. Anyway once I got it back together I had 90 mins of the loosen, twist, tighten .. revs up...loosen... revs down. Go to other bolt etc etc. Finally got it back to 750rpm and it is actually running nicer now than before, picks up a lot nicer. Result!
Another job that doesn't scare me any more hahahaha. I have a spare FIP ready to go with Viton o rings and gaskets in due course and no more dripping diesel
None of this would have been possible without various forums - thanks to all.
Oh and I still have no idea how you tap the pump to advance or retard the ignition. Do people use an old toffee hammer? There's no room in my engine bay for a hammer without it getting stuck on everything 👍

Correction: EDC FIP