It's been I guess five days now and alternator #4 is still holding. I've been driving the car using minimal electrics and I think that may be a factor. My cigarette lighter voltmeter came in and I've been playing with it a bit, turning on different electrical systems and seeing what happens. The biggest drop by far is turning on the cabin blower motor. All my testing was done at freeway speeds. It's a 240d so I've got three fan speed positions. Turning from "off" to "1" results in a drop from 14.18vdc to 13.80vdc. I thought that was excessive considering that turning on my headlights drops from 14.18vdc to 14.07vdc. Curiously, turning the fan speed to "2" only drops from 13.80vdc (@ speed setting "1") to a 13.70.vdc. Then turning the fan speed to "3" results in another large drop, to 13.35vdc. Turning on the A/C results in another .05vdc lost, so the electromagnetic clutch seems to not be a culprit. Eventually the aux fan turns on but because I've not isolated it I don't know exactly when it's happening so I don't have reliable readings for it.