Hi T6rs,
Here's a quick run down of my experience re cabin heat/air con eventual fix on 120K mileage Shuttle.
Initially bought and fitted PVC printed, then ally actuators, with new motor. Plastics broke but ally worked for a while, then airbox connecting link arm snapped, forcing buy of new airbox. Whole dash had to come out to replace, which trusted mechanic did, due to no space and time to do, on my part, so ££££ spent, but job done!
Inspection of old box revealed cause, in my opinion - design fault, or usual timed obsolescence!! Box flaps rotate on spindles, housed directly in PVC pockets, with nylon, washers. Some flaps moved smoothly, no problem, others very stiffly, due to regular use, which I would say was reason for actuator/link arm breakage.
If I had had the time and space to access, I would certainly have lubricated bearing points with a temperature rated silicone grease and fully renovated unit, renewing broken parts, solely. Mechanic did say that new airbox was better design, which is perhaps of some small benefit.
Hope the above is useful to anyone in same boat. Cheers.