Total time on drive was 20 hours.   Steve noticed the problem as an oil leak from the input shaft oil seal.  Internal inspection showed the input shaft thrust bearing roller cage which is a polymer cage to be partially melted and most of the rollers were out of the cage.  Overheat was the obvious cause of cage failure.  Rear race of bearing was seized on input shaft and was 'blued' from heat. This allowed the shaft to move back and contact the adapter plate.  All sorts of nastiness resulted from this but the details are not as important as the root cause.  Amazingly, the drive continued to operate normally but the time between roller cage failure and discovery of the problem is unknown. The oil passage from the input shaft pilot bearing to the thrust bearing was found to be clogged and no oil was getting to the thrust bearing (except for incidental splash).  What caused the clog has not been determined.  I will attempt to carefully grind away the input gear and see what it was as time permits.   
The rear race was spinning against the adapter plate and acting as the thrust bearing while being lubricated only with splash.  That Mobile 1 is amazing stuff!

A careful inspection of the gears showed no evidence of damage or wear.

Corrective action:  Replaced the input shaft assembly and thrust bearing, installed nylon snubber/spacer to bring input shaft endplay into spec.

Tracy Crook,   RWS