Brian,
(I was going to suggest the same thing...)

With the suggestions so far from the list I'd suggest you carry and extra
Dist. Cap & wires on you next trip and see if that isolates your problem...
it sure would be nice if that was all their was to it....
And some HEET for the tank if your gas tank sits at half full normally.
These gas tanks are said to build up condensation.

                         Mtngal

Help me solve this mysterious problem.
  Here are the details... was being subjected to torrential, monsoon-like
downpours of very heavy rain...