From here:
Selenium rectifier - Wikipedia
the forward voltage drop is 1 volt per plate. Each plate can withstand a reverse voltage of 25 Volts, but I don't know how many plates were used in the ZW. (I suspect either 1 or 2.)
I increased the forward voltage of my diode to 1 and then 2 volts in my simulation, but that didn't help. The only thing that does help is increasing the value of the 1.5 Ohm resistor. That low value was always suspicious. I need to measure them resistor in my ZW.