Hi Colincool

I am not an EHX tech but I happened to have the same issue as you had, even with only the trem reverb functioning and everything as you described. I was terrified this would be a hardware problem as I am out of warranty. However, to my surprise, simply resetting my Oceans 12 has solved this problem.

1. Power off your Oceans 12
2. Press down and hold the Preset knob
3. While still holding the knob down, power on your Oceans 12.

This will erase all of your preset settings which is kind of crp, but my channel B got fixed from this.

Hope this helped