I can't speak to sources for glyptal, but I can answer the thermosiphon question.
Thermosiphon has another (more accurate name): gravity circulation. It depends on the change in density (specific gravity) of the fluid when heated. Hot air (and hot air balloons) rise because they're less dense than cold air. Ditto smoke in a chimney, or hot water in a cooling jacket, if you give it a chimney (mostly vertical pipe above the jacket outlet).
To answer the question of thermosiphon with a particular fluid, you have to find out what its change in density is over the expected operating temperature range. Larger change is better.
Now for the bad news: Brake fluids are usually designed to have a small change in volume over wide ranges in temperature (to avoid hot brake locking, burping master cylinders, etc). You'd probably need a significant additional vertical pipe run to get enough motion to do the job.