Yeah, I figure it would be penny wise and pound foolish to try it out, so I've mixed up a fresh 25ml. 2 years ago I mixed up 100 ml, and barely used a tenth of it. Might have used half, if my life hadn't kept interfering with my photography. I'll stick to 25ml at a time from now on. Can always mix up more if I use it up before it's best-by date.
Turns out it is sunny this afternoon, rather the the rain that was predicted. I'm gardening while the FO cools and (hopefully) finishes dissolving.