You were right.. It wasn't the solder. I took the Octatrack apart and found the metal tabs were loose. I pressed them back into position and added a small bit of epoxy to keep them in place. It worked... sort of:
http://www.youtube.com/watch?v=VqU2nqG6L4IThen a month of use went by, and 3 live performance. (after all, this is a Performance Sampler, no?)
In the middle of my 3rd performance, before a huge audience, one of my encoders failed!!!
I took it apart after that gig, and found that the traces under the encoder top had a gotten moisture / perspiration. I assume that possibly salt, from the perspiration had fouled it up. I attempted to clean it out with contact cleaner, and reassembled the machine. But alas.. the values are not consistent and jummpy.
I am waiting to hear back from Daniel about replacement encoders.