Yikes, that's rough. I've had the exact opposite happen, honestly. Used the white Permatex high temp stuff on a steam line years ago and it's still holding. You sure it was rated for the actual service temperature? Some of those "high temp" labels are pretty optimistic.

The cheap ones can actually be dangerous if they fail. I learned to check the rubber for any tiny cracks or dry rot before trusting it with heavy glass. A little water or glass cleaner on the cup makes a huge difference for the initial seal too.

Packing a ring of damp clay" is such a smart fix. I would have just stood there staring at the fire getting cold, like an idiot. Do you think regular dirt would work, or does it have to be clay?