Bill, as usual, hits the spoke on it's head. There was a year+ of spoke wire production that was poorly controlled. Spoke would break along their length, not at the head or thread as is typical. Often little black spots were seen and many think these were the points of corrosion or some other issue that was manufactured into the wire. I've been involved with replacing many dozens of these wheels over the years and still see a few a year.

As all the wheel's spokes are suspect and given the age the hub is too by now I suggest the best long term fix is wheel replacement. Before I would just replace the spokes I would want to overhaul that hub to check on it's condition. In our shop the overhaul is $20 (ft hub, rear is $28). Then 36 straight gage spokes will be about $90 and the build labor about $70. So about $180 vs about $65 for the new wheel (installed and ready to just ride.) Andy