To add to this, we closed all other zone valves off and drained "everything" out of the offending zone. It actually sounded like when the water stopped, we had a pocket of air up in there somewhere but left it open for a while and nothing else came out so we shut the hose fitting valve and let the circulator run (first with other zones closed and then with them opening and calling for heat).
Before we did the final drain I took temp readings on the fins of the baseboards. There are 4 involved and frankly, we've always thought that the area was too big and needed more especially in the front of the bedroom with the dormer window where the floor is always cold. Anyway, in the mater bath, which is the first radiator off the boiler, I stopped reading at 140 and still going up, the one in the master closet, just about the same. Out in the bedroom, big radiator on the outside side wall, it was about 10deg cooler after the same period of holding the thermometer there. Then I tried the last radiator in the leg, in the front of the dormer where we always think it's cold, about 115deg there... still creeping up but not much. The boiler is set to max = 180, min = 160 so I'd expect to be in the 150deg range at the farthest point out figuring for heat loss through the loop and I actually took a reading in another zone and confirmed that (probably anecdotal tho). For right now, we put everything back to normal to see what it does. We have had really cold temps before and don't recall having this happen. I'm wondering tho if going to a max of 200deg on the boiler might help? It'll run longer but then temp won't drop as much over the run and perhaps help?