When I was fixing old cameras, the "Fix Old Cameras" Youtube Channel was a solid resource:
Late-90s cameras like the Nikon F100 are a different beast entirely. The only thing worse are probably compacts from that era like the Olympus mju. If something goes wrong there you can essentially give up on fixing it.
For me, the details of the Fix Old Cameras videos were less important than the approach and attitude applied to the problems.
But like I mentioned, I am not down the camera repair rabbit hole anymore. In part because of the intractability of many camera repairs.
I switched to servicing musical instruments. It’s a much bigger market, much less collector focused, and often $1000 is not a lot for a musical instrument but a lot for a camera.