“Could it be stale diesel fuel?”
Most likely. Stale, separated wax, bacterial growth, etc. Diesel doesn’t store well at all. They were crazy to be using diesel power for backup generator purposes anyway. They should have been using propane-powered units. Totally trouble-free.
I am skeptical of the explanation of salt water contamination given in the news. That explanation is not contained in the TEPCO press releases to date.
Per the original maintainence schedule, the Fukushima Dai-Ichi 1, 2, 3 BWR Reactor Core Isolation Cooling systems should have been tested every three months...
Totally trouble free until there's a 9.1 earthquake and tsunami. Maybe they should have used wind turbines for the nuke plant's emergency power.