I used to tell people I didn’t work on spring reverbs, but I guess now I do. So this reverb unit had its whole B Channel not working. It turned out it was just because of cold solder somewhere on the board. The solution is simply to reflow and add solder. The power supply capacitors also had really leaked a lot. Replacing those made the output a lot less noisy.
This so-called “stereo reverb” is not stereo in the sense that there are two springs or two independent signal paths. The left and right sides of the stereo channel are just inversions/180 degree phase shifts of each other.
Interesting little note about the signal path here: If you send a signal into the channel B input but there is nothing plugged into the A input, the A output will be just the reverb from the B signal (100% wet signal). This is because, like I said, there is only one reverb signal, which picks up from both inputs and sends to both outputs. But this sooper mooshy sound can be kind of fun to play with.