[jku72]

I never tried the brake fluid, but....
I have unsiezed some very siezed engines, including the following: a 40 chevy 216 that sat from 1962-1997, a 43 willys flat 4 that sat for 5 years, another 216 that sat for 20 years, and a 223 ford flat 6 that actually as it turned out was blown.
The thing I have had 100% success with, is a 50/50 mixture of liquid wrench and marvel mystery oil, filled the cylinders and intake untill over full, replace the spark plugs, and wait about 2 weeks, no rings stuck, everything loose and fine. plus, the oil seems a little friendlier than brake fluid, but maybe not, I am not suggesting that method is not better.
Good luck whichever way you go.

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jku
70 C30 CST Longhorn
68k10 burb
69 K5 beater
43 willys GPW
40 Chev coupe
67 catalina