On all digital meters that I have seen, the diode test mode measures the voltage drop across the diode in forward and reverse direction (when the leads are reversed). The foreword drop through a germanium diode is usually around 0.3 volts and “OL” in the reverse direction.
Your readings, IMHO, are inconclusive but I would expect more resistance than megohms (usually OL) in the reverse direction.
Do you have a new 1N34 to test?
All of the HV caps in my set are ceramic, but higher than spec value...no problem. I suspect that your poor sync (flipping) is likely caused by the weak video signal... when you get decent contrast, sync should improve.
jr