So how did I know about Subaru and leak stop? Because I have one!! It turns out the 1998-1999 2.5 litre engine has a bad history of blowing head gaskets. Sure enough, mine blew! Because it's infrequently used (mostly for pulling a small trailor around and when 4 wheel drive is required) I don't want to spend any money on it.
Bars Leak HEAD GASKET sealer to the rescue! It's a several hour project following directions, which are quite detailed. Following the treatment, the last step is to drain and LET SIT for 12 to 24 hours for the chemicals to cure. So it's like a two day marathon. Success! No bubbles in the radiator, no over pressure in the cooling system, temperature holding steady.
...quick, sell it!
Nah, I think I'll keep it and call it a "long term" test of the product, so far so good. But then again, I don't drive it much so, who knows.