Questions about a Motor Starting Capacitor

My garage door opener stopped working; it just hummed for about 2 seconds.
For no particular reason I touched the starting capacitor and fixed it. It
ran okay for a couple days, then stopped. I touched it again and it ran
twice before breaking. Now my magic touch fails completely. (I can't find
any loose wires)
The manufacturer's best guess is that the capacitor is bad.
It takes a 53-64 mfd 220vac 30b0363 Fujitsu Towa no. gk-86
1) Any way to varify the capacitor is bad before replacing it? I put an ohm
meter across it, and it shows an open circuit, but since I have never tested
a good capacitor I don't know how much that proves.
2) The manufacturer wants $20 for a replacement. Am I likely to find one
cheaper locally? Where, an electrical distributor?
3) There are two red wires going to one contact and two blues going to the
other. Is a capacitor symetrical, so if I got my contacts backwards it
would be okay?
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There is no polarity to that sort of capacitor. I have had them fail internally where an aluminum strip connects to the wound plates. Your best bet is to replace it.
The value is not that critical and if you don't mind having a larger capacitor mounted outside the case, get a metal cased starting capacitor from an air conditioner or similar. 40 uF will do the trick. Make sure the voltage rating is at least 220 VAC. Again polarity is not a problem.
The trouble with yours is that it is non-polarized electrolytic, to make it very compact for its capacitance, but much less rugged than a normal non-electrolytic type.
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Do you have an analog Voltmeter? If so put it on ohms and measure one way until needle stabizes near open (infinite ohms). This should charge the cap with what the VM supplies to test resistance. Then reverse the leads. The reading should be less than open (maybe even near zero) and move to open as the cap charges to the other polarity. If it shows open right away, it is probably toast. An digital meter may do the same thing. But I just put mine on capacitance an measure directly.
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