Geeze, how long do think people are leaving these flush chemicals in for? And what chemical?Chemical flushes will erode the insides of your steel coolant lines, eat the aluminum oxidation from the aluminum parts, exposing pits and potential leaks,
The most common seems to be citric acid, and Thermocure doesn't contain any acids. You should be able to run Thermocure as long as you want without damaging any metal in your cooling system.
Also, if there's a leak that's only been sealed by corrosion or sealant, I would want to know about it.