We had the same problem back in December 2012. We posted about it at that time. Same way that you describe your situation. We are still adding 52,103 to our mileage log to account for the "lost" mileage. We ended up adding a new ground wire to the dash and the problem has not reoccurred in all this time.
Shortly after the odometer changed itself, we started to experience flickering with the a couple of the other gauges on the dash. That is when we decided to add another ground wire. Knock on wood, neither the problem with the odometer or the other gauges has returned since adding the new ground wire. The odometer is continuing to accumulate mileage correctly from the new odometer reading from that date forward.
For what it is worth, when we were researching the problem back in 2012, we were told that bad ground and flickering gauges were a known problem with Monaco Dashes and since Holiday Rambler was manufactured by Monaco in 2007, stands to reason you might have the same problem for the same reason.