Do you have access to a cooling system pressure tester? I'd suggest pumping the system up to within a pound or two below the pressure rating of the radiator cap (probably 13-14 pounds) with the engine warmed up to operating temp and then shut off, and look for seep leaks as it cools down. I've cured small leaks like that by draw-filing the gasket surface of the thermostat housing on occasion. It might be warped slightly so the gasket isn't sealing equally across the whole surface.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
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