ZC,
You are looking at a typical 9001. Effectively, they all have a channel or two out, and if they don't when you buy it, they will soon. This is caused by a dual sided PC board that all the quad mode switches mount on. Dual sided boards were new in 1976 and they hadn't worked out how to connect the two sides, and cold solder joints develop in the "passthroughs" the places where connections are made between sides. There are 54 pass throughs on this dual sided board. It is the bane of the 9001.
Fixing it is not easy and is beyond the confront level of most techs. Also, because the unit is almost 35 years old, you might as well have all the electrolytic caps changed out for new ones. Their spec'd life was 15-20 years, and even though most of them still pass audio, the sound is nothing like what it was when new.
As far as what it is worth? Practically all 9001s are repairable, because the quality of the internals was probably as high as anything ever made in Japan in the Golden Age. There are gold plated connectors throughout. The pots and switches are very high quality, and the asssembly was first rate. The price that 9001's sell for is almost completely determined by cosmetics. A like new unit with no scratches on the panel or the cabinet, with documentation and 4 ch test record will go for as much as $1250. An average unit in good condition with some scratches and chips on the cabinet and no bad nasties on the panel will go for $250-500. That's pretty much the range.
My son and I specialize in restoring 9001/8001's. You can see pictures of the dual sided board and what's involved in fixing it on our site. QRXrestore.com
Jim