I figured I'd update this thread in case anyone was interested.
I went ahead and authorized the repair. I was already out $160 for the diagnostic, $115 for shipping, and would pay another $100ish to have it shipped back. Then if I found a different repair center, another $100ish to ship it to them. So even if I could find someone to do it for $800, I had $475 in sunk costs making it close to a wash and exposing me to extra risk in shipping the amp all over the place.
The repairs appear to be done well - everything inside looks clean and well put together. The large filter caps are now Nichicon, so at least decent quality. I hooked up the amp in my second system and it is working fine. Hard to say if it sounds better since I haven't heard it in two years and my second system is a home theater. I will eventually try it in my main stereo system but literally every component in it has changed since the last time I used this amp so that also won't be an apples to apples comparison.
In the end, I wasn't ready to just "throw it away" so even though it was a lot of money, I was basically backed into the cost corner already and thought it was better to have the amp working perfectly again. I do appreciate the feedback I got in this thread. In the end, I'm sure I overpaid for the repair but based on my sunk costs, that was basically inevitable. Lesson learned and at least the amp should be good for another couple decades. In the long run I'm not going to regret it.