Yayyy!! Found my coolant leak, and a few other things lol! For several weeks have been gathering parts to replace all the rubber hoses under the manifold. The last one finally arrived today, so set to work. Ever since I got the car I've been adding a couple ounces of coolant every couple or three weeks.
I'm relieved to discover ample evidence of a leak from the head-heater core hose junction (and a split starting in that hose). I also found several loose coolant and air hose clamps elsewhere under the manifold-- the result of idiot mechanics or hose shrinkage with age -- I don't know. This poor car has been neglected -- the coolant that came out was very dirty, and when I took the drain bolt out of the block, nothing came out (?) So I stuck a coat hanger in the hole and wrangled it around until I got a gusher lol.
So the moral of my story is, if you haven't been under the manifold yet, and you don't have records to prove that someone else has, get under there now, before you blow a hose and overheat the motor! I got mine in time. . .
Edit: looking down into the cylinders, can still see the cross-hatching: pretty good for 197k miles.