I've had good luck with them [Adcom] over the years. Back in 1989, I bought a new GFP-555 preamp, GFA-555 Amp, and GFT-55 Tuner (still have them all.) I've contacted them with some tech questions, request for service manual/schematics, and parts; it's been easy to get in touch with a live person. They changed ownership and moved to Arizona a few years ago, and I think some of the spare parts inventory for the really old stuff might have been tossed in the dumpster in NJ. But they have very nice trade in deals, not just for their stuff but other brands too (offered after they didn't have replacement volume pots for the preamp.)
Lately I've scored several other pieces on Ebay. Their gear holds its value well, but seems a bargain compared to when it was new. I just picked up a GDA-600 DAC (for the heck of it) and GFA-5200 amp for a new bedroom system I'm assembling.