You should be able to feel play in the hinge after 1,000 hours. Expect door wear too.
I replaced hinge with baffle rubber and fabricated new door. It's showing wear again one thousand hours later
Me too, and ditto! My carb heat door is currently in real need of replacement.
Green gunk is most likely fule dye, probably would be a good idea to blow it out.
I ended all the issues with the wire Push Pull cable by going to a cable with a threaded end. I use a rod end fitting. No Mickey Mouse issues. This is an important control and this isn't a place compramise.