I've already pulled the two front wheel sensors, cleaned and inspected and replaced them. The resistances were within tolerance and they generated a nice ac mv when the wheels were spun. The rear sensor was tested as I mentioned above. In my case, the problem is likely underhood heat related. It could still be a sensor, but they look okay so far. I don't have a scope (and haven't used one in forty years), but if I did have one, I would certainly like to see the waveforms.

If I knew someone in the Atlanta area that had an older Bosch ABS tester, it would be worth a try. My 1986 M-B tech data book lists the outcomes using the Bosch tester. It apparently plugs in series with the ABS ECU and the connector.

Thanks all.

Brent