Well, I am glad to report that after a few hours work and a trip to recycling centre to dispose of dirty diesel that Astraeus is now cleaned up and running again. New filters and cleaning out tank and pipes has done the trick. Had her running while on her berth for 45 minutes. (under load)
New spare filters ordered to replace the ones I have used. Have also ordered some new diesel bug additive.
I think I have found source as well. We had some very heavy thundery rain. The filler for my tank is flush with floor of cockpit. The seal around the tank filler cap, s not in good condition when looked at closely. So that needs renewing too..... and closing with a good seal of Vaseline round outside of cap.
Next time boat out of water this stupid design is getting raised a couple of inches. This possible as cockpit has teak gratings with sufficient clearance.
New rule on board.....
Check glass water trap on primary filter before every trip.
Chris