Risk in owning used McIntosh amps?

I am about to take the plunge in purchasing a pair of used Mcintosh monoblocks. Before I do that, I would like to seek advice from other owners of used McIntosh amps. Since the warranty does not transfer, what should be done when there is any problem? Are there other qualified technicians, especially in the San Francisco bay area where I am located, that could service the amps? I thanks you in advance for your feedback.
best regards...