ouch. seems to be par for the course nowadays, though. I've got 2 pieces of (non AR) equipment out for manufacturer repair at the moment and one is approaching 1 year since I had sent it in. 6 weeks and counting for the other.
I think they are user-serviceable, depending on the user.
Kudos to you both for taking it on. Looks too involved for me.
I'm happy to hear you are back up and running without having to send the amplifier in.