Thanks Mark, It’s always worthwhile to hear an informed opinion.

I got this into the workshop yesterday. All the engine pipework is holding 1 bar with no drop (I use my cooling system tester for this type of test). The only thing I can see on it is a very slight sign of a weep on the supply pipe from the tank. I think it is too small and too dry to be my problem and to investigate it further the tank would need to come down. I suspect I will be taking the tank down later.

Of course this has not failed to start except the one time I mentioned earlier.

I have to wonder about pressure testing a system like this which normally works on vac. A hole in a pipe would show for sure but a weak seal might shift under pressure. Considering how bad these are, eg bleeding after fitting a filter, any that I have ever vac tested have shown a number of leaks from O rings but under pressure don’t leak.

I will see how it holds a vac later and wiggle test the connectors a bit at the same time.