Man oh man, @richardh44 you hit the nail on the head there. A buddy of mine spent a whole weekend scraping out an old frame only to find the channel had a hairline crack he missed, then had to swap the whole thing anyway. He said he would have saved himself the headache if he'd just checked the metal first like you said.

That inch of glazed creosote you pulled off, was it from a wood stove or an old fireplace insert? The reason I ask is that I've seen those 9-inch poly brushes with steel bristles really shine on the heavy stuff, but they can scratch the hell out of a stainless liner if you're not careful. I had a buddy who swore by his dad's setup too, but he gouged a cheap liner so bad on a job he had to replace it for free. So I wonder if that old school performance only works because the flues back then were built tougher, or if we're just babying our gear too much now. Maybe it's just that the new liners are more delicate and the brush needs to match them, not just the soot.

Did you have any trouble getting the shim to stay in place while the glue dried? I had a buddy who did basically the same thing for a squeak in his dining room, except he used a plastic shim and construction adhesive. He said it worked perfectly, but he told me later he forgot to clamp it or hold pressure on it, so the shim came loose overnight and he had to go back and do it all over again. He ended up sticking a heavy cinder block on top of the spot from above for a few hours until the glue set. Made me laugh because he was so proud of that fix the first time.

Man, that's a good point. Inflation alone probably would've made that refund worth a lot less than the tent you actually wanted.

Honestly, have you tried aeropress yet? It's that weird middle ground where you get cold brew's smoothness but with hot brew's complexity, totally kicked my chemex habit too.