Ok, re the engine problem, remember I said it was in a Privateer (O/T). First point I actually owned this device before I gave it to my mate so I considered myself lucky when this happened.
Old Fart you got it right it was the tank, a metal one that had corroded away in one corner. The give away was when the wing was taken off and the plane was being "placed in my mates car" he got wet feet from the fuel that flowed out of the fuselage. % bottle of Johnsons baby powder later plus numerous harsh words and a surgical removal of the tank the actual cause was discovered.
Food for thought, things aren't always what they seem. BTB the tank was at least 10 years old.