Hi Dave, like everyone else sorry to hear about your coolant leak.   I once came out after a cold night and  found coolant beneath my aircraft by the exhaust and I figured that the coolant  "O" rings were leaking.  Decided to fire up the engine anyway, coolant leak went away and never came back.  The only thing I could think up that might explain a "temporary" leak was that the "O" rings had "shrunk" due to the cold sufficient to allow a small leak.  Not a very satisfactory answer - but since I know you will be trying to figure out where the leak is coming from wanted you to hear it.