Helpful hint that you may already know.
I apologize in advance if many of you already know this, but I thought that I would pass it along just in case it helps anyone. I develop primarily in Microdol, which requires mixing at a high temperature. I develop it 1:3, which usually leaves me with a fair amount of leftover. I always parse out the developer in empty plastic Coca Cola bottles because I assumed that they do not breath at all. I fill them ALL the way to the top and cap them tightly. This has worked very well and developer has lasted full in these for months. My only dilemma was what to do with a half empty bottle. Well two months ago I took a half empty bottle and simply squeezed the sides until the liquid level reached the very top and then capped it. It kept that squeezed form. I developed using that developer 2 months later and noticed no difference. I bit easier than marbles. Just another idea for you guys.
Sudden death has a non-XTOL cause perhaps?
I've made several five liter batches of XTOL stock with distilled water, and use marbles to minimize air. I've not seen the sudden death yet, and wonder if there's a water impurity or oxidation trouble. I've a friend in town who uses it exclusively for her B&W work without horror stories. I've used eight month old XTOL as well as the no longer recommended 1:2 and 1:3 dilutions. The times I've had troubles are times I messed up something else. I can't prove it won't happen to me, but I do wonder if something else in the worker's environment results in a clock reaction causing XTOL to lose potency.