There is a simple way to test the old one...blow into it and then suck on it! If the diaphragm is good, you'll get positive resistance when you blow and suck and will feel it hit its stops. If the diaphragm is bad, you'll be able to blow or suck air past it. You can do it with a Mityvac pump, but the lips work just as well. Back in the day when cigarettes were more common, I've seen folks blow cigarette smoke into the vac advance. If smoke came out, it had a bad diaphragm.
Matt
