Roger, I have the same fittings as you and the leads were very difficult to remove. It's hard to understand how so much water got in and I've never seen any even when I have checked after being out in the rain. On this particular day the car had been running perfectly for hours before finally misfiring so why didn't the water boil off ?
This is a bit of a conundrum and interesting that you also did not see any water after being out in the rain. The short answers is I really don’t know but I’m always up for a guess
My money is on the internal seals between the plastic rocker cover and cylinder head (around the plugs). I bet these are not gas tight when there is a pressure differential. They may breathe a little when the engine is running and the crankcase pressure is raised allowing humid air into the semi sealed plug cavity. Then as the engine slowly cools condensation forms on the plugs and adjacent aluminium surfaces (assuming external ambient temp is low enough – this might be a winter thing). Any water is then trapped down in the plug well. This cycle is repeated and a little more water accumulates.
The water/steam can’t boil off as it can’t escape easily. It struggles to get back past the rocker seal as there is positive pressure behind it. So the only way is up and out through the internal hole in the rubber plug bung, past the HT electrical contact. Perhaps in your case Keith you collected the critical amount of water and it took a couple of hours for the pressurised water/steam to work up the lead and cause the miss fire.
Re your excessive corrosion perhaps it not just water? Wouldn’t the crankcase gases contain nitric acid vapour and other nasty’s?
That’s my theory for what its worth!
(please feel free to debunk it).
Anybody got another?
