Two of my students today were visiting a local hangar that has a P-51, AT-6, and other types in it. This is third-hand, so take it for what it is worth.
The owner told the students that he knew the foundation and the crew of the accident airplane. Supposedly, it needed new fuel bladders, but they couldn't get any. Instead, they built aluminum tanks (this may mean that the wings were converted to wet-wings; not sure).
He guessed the wet wings/aluminum tanks may have leaked onto the turbochargers, which for engines 2 and 3, are well aft of the firewall.
From the pictures, that looks feasible to me.