As you probably know by now, they are out of production. There is a 'fix' for them, as most of the failures occur in the control buttons on the board. There is a procedure to clean them and get it working again. I'll dig around in my files and see if I can find it.
As you probably also know, if it is not 'fixable' and you can't find a replacement, the only other option is to convert both of your Dometic roof units to a 5-button compatible relay control board and to change out your 4-button t/stat for a new 5-button model. This modification is a bit pricey, though.
Lew Farber...RVIA Certified Master Tech...ABYC Certified Master Marine Electrician
SOLAR TECH ENERGY SYSTEMS, INC.
AM SOLAR ...MAGNUM…VICTRON ENERGY...LITHIUM & LIFELINE BATTERIES…MARINE REFRIGERATION