I have a goodman a/c I replaced the capacitor about three months ago and found the samr problem today, can anyone tell me what might be causing this problem.

The Voltage Rating needs to be greater than 240 volts, most I see might be 370 volts, fine, just can't be less. Maybe bad batch. I would replace. Try another source for Capacitor, if that goes out. Hopefully more input will follow, concerning cause.

I replaced the capacitor with the same voltage rating which is 370 and 30 uf / 5 it is still going bad.

Is this proper size for the fan motor ? Was motor replaced? What is going bad on the capacitor ( the fan side or the compressor side) this capacitor serves both. And I will say that the capacitors built today are not as good as the ones built 20 years ago , Mike

Replace with 30/5 440. This is stronger. As acetc mentioned, they (as everything else) is jjust not made like they use to be.