Well, this is embarassing.
So, my old radiator hose was leaking like a sieve, so I replaced it.
In the process, the thermostat housing cracked.
I replaced the thermostat housing (and thermostat) and sealed everything up.
Problem is, even with the hose clamp tight (I'm afraid to tighten anymore, with the aluminum T-stat housing), I still get a slight hiss of pressurized coolant that comes out. It is maybe enough to wet a postcard, each time I stop.
Can I put gasket sealer around the bottom of the hose to stop this, or is there some trick I'm missing from the Jeep world?