Last time I had to remove the high-temp stuff from the threads of SS
bolts in a boat motor, my Dad (an A&P for 35 years) made me use leaded
MOGAS. That was in 1979.

That loosened everything up, but I still wound up peeling most of it
off of the bolt threads, and then hitting it with an SS wire toothbrush
dipped in gas, followed by a red shop rag.

Knowing what we know now regarding shop safety, I don't think I'd go
that route again unless nothing else worked. And then, I'd be extremely
careful. Gasoline has some very nasty properties when it comes to vapor
pressures and flamibility. Maybe just a soak in a small amount of gas
poured into a coffee can, placed squarely in the middle of my
vegetation-free back yard, followed by a rinse in something less
flamible.

Harry