"I have these brakes on an 85 Ross Mt. Hood. My winter commuter. The rear brake is mounted on the lower chainstay - where it's hard to reach and gets filthy when riding in the winter..."

that is why, aside from them being cheaper, the manufacturers went to cantis on the SS. I think your best tool here is just patience. I have not worked on one of these for sometime but IIRC you loosen the 'arm' with an allen and adjust the spring tension with the cone wrench then tighten yes? it is just a matter of delicately adjusting one and tightening it. then adjusting the other. my U brake is like that and I hate it. if you are only talking 1 - 2 mm of difference I would not worry about it.