Honestly, seemed fine. And the idle being controlled, steady, and slowly dropping until it settled out at approx 800rpm (maybe a shade under) was a good sign. I just looked at how long I'd spend finding something that was the right
sort of thread, then finding O-rings, and thought "well what if..." and there we go. Just a good turn around each to ensure a good seal, and that was that.
Will remove and block the T-piece first, then the single one. That should narrow it down straight away. Fingers crossed for the 'single' pipe, as that's narrowed down to one thing straight away!
Ok, so to add to info. For the first half a minute maybe of running (engine was pretty much up to temp btw) there was a slight whistle. The best way I can describe it is being like the comedy whistle when people are snoring in cartoons! Literally, approx 4 every ten seconds. So eg: 2.5secs quiet... 2.5secs whistle... 2.5secs quiet... etc...
I'm going to hazard a guess and say this is one of the 'bagpipes' only a hunch. Now whether this is air escaping, or normal operation, I can't say. Appears to be rearward, at the bulkhead.