I spotted the oil after a cold snap, but could not get under the coach to find the source.

Thanks to members advice, I drove the bus to a truck/bus repair garage.

The educated guesses that the leak might be a failed wheel seal were correct. This led to replacement of the rear brakes, differential oil, and wheel seals all around. $$$$, yikes!

Thanks again everyone. Beware importing a pampered cupcake coach from its desert home into the cold, rough tough northeast.