I'm using the Tetenal C-41 3 bath kit, and have been using my working solution far past its advertised life in terms of calendar time. However, I haven't run too much film through it. I store it in collapsing PE bottles with the air squeezed out, so not perfect, but not terrible in terms of oxygen exposure during storage.
So far the old working solution keeps on working. In the past I've just thrown it out when I approach the recommended keeping time, but being a bit curious and perhaps a little greedy, I've decided this time to keep on using it until it fails.
What are the signs of imminent depletion? Does it fail all at once, or would I begin to see reduced quality? Does the developer fail before the blix? (My water based prewet is used one shot - I'm not THAT greedy! )
I'd like to see how long I can continue to use it, but cringe every time I introduce new film. I would mix a new batch but I'm just too curious, plus I'm not developing anything I couldn't afford to lose at the moment.