Well, I drive the coach to get it washed and gas it up. When I came back, the right brake light wasn't working again. I dug into the steering column again and took the connector off the turn signal switch to take some ohm readings with a multimeter. I found that one of the male spade connectors that outputs the right brake signal (it's the connector that would mate up to one of the green wires on the plug from the harness) had 0.1 ohms when wiggled one direction, and then increased to over 100 ohms when wiggled the other direction.
I replaced the turn signal switch assembly ($142 from freightliner) and the problem is now completely solved.
For anyone needing to replace their own turn signal switch, it's a pretty easy and straightforward task. There are only two torx head bolts that are needed to be removed. I used a torx bit which I turned with a adjustable wrench as the clearance below the steering wheel is tight.
Thanks again with all the help and suggestions. Hopefully this helps someone else out somewhere down the road.
2006 Thor Mandalay 40F, 400 Cummins ISL, Freightliner Chassis.