I've never run into anything like this but now you've got me a bit worried. I have a 300 gallon tank. I go through about 100 gallons a year.
100 gallons is the min they will fill so I get them to fill up 100 gallons each year when I see it gets low. Just had it filled and dumped a powerservice bottle into it.
Touch wood three years that I have been doing this now and the diesel seems to be in decent condition.
I did add a water block filter to my pump so perhaps the combination of that and the PowerService that I add is helping. I don't think you could get much more stale than mine though sitting around for a year.