All of my transformers that failed shorted primary to convergence. The quick way to ID it is the two 2.2K 2 watt resistors in parallel start overheating and vertical goes crazy. It appears to puncture the insulation. I have one of the bad ones and hooked it's primary to 120 volts AC. It works as a stepdown but leaks to convergence windings.

I had an RCA (CTC-16) that did short primary to frame. I was not smart enough at the time to try just isolating the trans from the frame at the time, but then again I was able to get a new trans for it. the zenith is the one I did a video on the repair and it was exactly as your described, wonky vert then no vert, and open resistor (in my case a single 5w 1k).

for fun I tried to "burn" out the short, that video never got published, all it did was get worse and then finally opened the primary.