Thanks for the reply Lt Dan.
Fortunately there was no foreign matter found in the system (good news!). Once they got my rig in the shop and dug into it they determined that the bushings on the passenger side valve failed causing the valve to stick and break the linkage. Subsequently that linkage flailing around struck the drivers side valve and knocked the linkage off if it. Why the field mechanic stated both valves were frozen I can't say.
Resolution was to replace both valves.
If anyone in the Southern Oregon area needs mechanical work done on their DP I strongly recommend Northwest Freightliner
in Medford. I am not affiliated with them in anyway other than a very satisfied customer. They are just off I-5 in Medford. The shop is large, and I see motor homes there all the time, and service writers are friendly.
I recommend them because in late May I had an issue with the rear driver side air control valve, they were able to replace the valve and get e on the road overnight. When I contacted them last week from the road, they dispatched a mechanic who got me rolling and followed me to the shop. They then diagnosed and repaired the issue. Because I had recently had work completed on one of the affected valves they only charged me parts for one valve.
Three days in the shop, and two new valves for less than $100. Hard to beat that level of customer service.