So the selling dealer makes your coach "Like New" by repairing the rig with parts scavenged off another (or multiple other) unit. That is fine for the A/C or even the leveling system but when it comes to the braking systems, you need some sense of confidence in the ability of the system to operate properly.
Turning a three grand repair project in to a couple hundred bucks repair by possibly utilizing scavenged parts does not instill confidence in the ability of the unit to operate properly when needed the most, in the field.
If the A/C fails again due to the scavenged parts then all you end up with is discomfort inside the rig. If the parking brake fails due to scavenged parts used to repair it then the consequences could result in property damage, injury or even death.
If i have a manufacturer certified mechanic tell me the repair must be and can only be done properly in one manner and the selling dealer that is NOT manufacturer trained and certified telling me they can do it their way for a small fraction of the cost I tend to wonder who to trust and I am not likely trusting the guy that is cheapening out.