Where was the fueling done? Any other trace chemicals?
I start wondering about the level of smog in the air when the refueling was done -- what other chemicals might have been present at trace levels along with the "H2O" that could have catalyzed or been involved in causing the blockage to form? It's like the problems with trace contamination anywhere --- no single material may be a problem but combinations can, and the possibilities are enormous. Remember the cat and dog food problem? Two tiny trace contaminants -- but inside the kidneys they formed large crystals that blocked function and caused death. Something like that? If so we'll see more of it in the future.