Have you tried firing it even hotter than ^6? Like up to ^7 even though it's a ^6 clay? IMO it's worth a test (use a waste tray/shelf underneath just in case)
You mention you "can't see any crazing"....to a molecule of water or a tiny bacteria, a teeny tiny fissure in the glaze is like the grand canyon, of course it will make it's way through!
If your glaze is crazed, the glaze and clay body do not fit one another, their coefficient of expansion is too dissimilar. This is only part of your problem, the other seems to be lack of vitrification in the clay itself. For those experiencing seeping on thicker forms - this is because the thicker it is, the more heat work it requires to penetrate the core of that clay mass and bring it to full maturity - which is why reducing thickness via trimming the foot resolved the problem.
To test if your clay is vitrified: fire object and then weigh it. soak in water for 24hrs, dry it off as best you can and then weigh it again. calculate % of absorption from the difference.