I have one month left on the one-year warranty on the Mac Mini. I better do something while I still can.
I tried using the Apple website to book an appointment at the Genius Bar. Using Linux to do that proved difficult. No, not difficult, impossible. I pulled up the App Store app on my phone and had an appointment within seconds. That was neat.
I took the Mac Mini in this morning, checked in, and waited. Right on time, I saw one of the Geniuses come out with a monitor. Hah, I bet that's for me and the Mac Mini. And sure enough, she was. I had a diagram showing how the Mac Mini fit into the system, I had a timeline showing when the problems started, and when they occurred, and when I did a clean install. She looked in the Console and saw the history of kernel panics. I felt better, there was evidence and not just me making stuff up. She ran the standard Apple hardware tests, no problems found. She did a network connect and ran a series of inhouse special tests. No problems found.
She said she suspected the memory, or the motherboard. No, she really suspected the motherboard but wanted to test the memory first to eliminate that. She wanted to keep the Mac Mini for 3 or 4 days, run tests, replace the motherboard, run more tests. Okay, fine with me. I signed the order for the new motherboard, a little shocked at the $480 price tag. I balked at first, asking if I had to pay that. No, I didn't have to pay anything, the final price at the bottom was $0. That was probably designed to make me appreciate what I was getting. She took it away and now I wait for the result.