i think he said earlier that Pot 6 was within 10% of the others....
frankly, that piece of information bothers me.... i'd want it a lot closer than that..... if something happened valve wise previously, (assume it is somewhere in another thread) i'd strongly suspect something like a damaged valve seating , and i'm damn sure that would affect the running to some extent..... whether it would cause this issue, on it's own, i'm not so sure....
however, it strikes me that if an exhaust valve is damaged, even if it's just the seating , then the emissions light issue would make sense, as the thing will be leaking unburnt fuel mixture on compression cycle....
given that almost everything else seems to have been prodded and poked , changed, swapped, and tested, there's not a whole heap remaining....
ultimately, the holy trinity of Fuel, Compression, Spark, are what run the thing, and if it's lumpy and grumpy, there's going to be a reason affecting their relationship somewhere.....
i'm not up to date with the control systems , but in my youth i did used to build competition engines for rally use..... 10% is a LOT more variance than i would ever have accepted on a compression test.