In the old days, Jaguar recommended Bars Leak be added with every flush and fill. If you've ever changed hoses on a Jag, you'd know why: 20 or more hoses, secured with pathetic Cheney clips. Point is, it's safe to just leave it in there. If there are no leaks, it just continues to circulate.

The one problem would be if your radiator is heavily clogged, in which case Bars Leak will ensure that you will need anew radiator.