[dmsfrr]

You can easily test the vac adv diaphragm on a dist with a longish piece of clean vacuum hose.
Connect one end to the canister then put the other end in your mouth and blow into the tube, it should hold pressure and not leak thru. If it leaks replace the vacuum canister. Sucking on the tube should rotate the points/breaker plate approx 1/4 to 3/8 inch (yellow arrows) it may need to be cleaned & lubed if it's stuck.

this example photo is of a '55 distributor but the principle is the same