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This is long but I hope the explanation makes sense. I’m guessing it will work for your 33.
The vacuum advance on my 34 Master quit working and finding a replacement was difficult. While I was looking, I thought I’d have nothing to lose if I attempted a repair. Since the defective unit could be stroked freely by hand, I assumed the diaphragm had ruptured. If you look closely the advance, the two halves are joined around the perimeter with a tight crimp. After some effort with a sharpened screw driver and slip joint pliers, I was able to separate the two halves taking care not to overly damage the mating surfaces. Inside is a spring and the diaphragm with the actuating tab riveted to it. I carefully removed the actuating tab from the ruptured diaphragm by grinding off the rivet. I had a new spare vacuum advance from a 60’s 6 cylinder of the same diameter. After disassembling the new spare, I used its diaphragm in the 34 by replacing its tab with the one from the 34. Rather than riveting the tab, a small nut and bolt worked great. Prior to crimping the two halves back together, I used a small amount of black rtv on the outer edge of the diaphragm.
As a side note, I think the starterator vacuum unit can be repaired the same way.
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