45 some years back I used a stop leak in an emergency to repair a leak. In days my pump gummed up and the system started over heating. I blamed the stop leak (do not remember the brand). But years later I had a issue on an old land cruiser with a head gasket again in an emergency I used some Bars, put 20k miles on it with out issues.
Being a stickler for doing it right I prefer to fix the issues with repair then patch but sometimes things call for patches first.
As for your non-pressurized system as well as how the BARS functions in the system take a look at the link.
http://www.barsleaks.net/product/bars-leaks-stop-leaks-pellets/If you select the red "HOW DOES RHIZEX WORK" you will find a open air tin can experiment that would be like a open system.
One of my old HIT-N-MISS engines had a few pin leaks in the water hopper, BARS did a nice job on sealing those.
