I assumed it was the voltage regulator (from eEuroparts with integrated brushes), and replaced the component rather than the entire alternator. These are the parts commonly replaced when you buy a "rebuilt" unit. However, the problem persisted. Using this advice from fellow Brickboarders (you can search for my posts about one month ago) the problem was determined to be the windings in the alternator itself. Because I had already invested the money in the regulator, I picked up an alternator at a local junkyard for $40 and put the new regulator in it (better than pulling the unit out again next year) and solved the problem for $100.