Another data point: some years ago, a large local camera store was downsizing and sold off all its darkroom inventory. I picked up an ancient, rusty 5 gal can of Dektol powder. I immediately separated it into a number of small glass Mason jars. The developer works fine, if I'm printing fast enough. If the stuff sits in the open jar for a couple of weeks, it turns quite brown and I toss it without trial. Unopened jars maintain their original color (more or less, I suppose).
Originally Posted by Thomas Bertilsson