I'm only in this forum because I had a 5100 that needed some work. My dad gave it to me about 20 years ago. I never used to use it as the volume knob only worked in 2 places and then for only 30 seconds before needing to be tapped. Several of the front switches were the same -- every few minutes I'd have to flip them a few time. I didn't get why people thought these things were good. My dad told me he thought it needed a recap when he gave it to me. I almost threw it out at an electronics recycling event, but decided to recap and deoxit it instead.
Well, it sounded so good once cleaned up that my crappy test speakers sounded better than they've ever sounded before. I hooked it up to my main system and was just blown away. I needed a remote, so I ended up getting a 6600 to replace my aging Nakamichi receiver in my main system. I still use my 5100 in my office.
If you look at this forum you can find the schematic and parts substitutions for most pieces of the 5100. The switches can probably be cleaned and conditioned no matter how bad they are. The pots maybe not so much. I think I rememeber seeing some threads here on now to rebuild the wafer using a new pot, but that may have been for a different vintage amp.