I was changing the heater core yesterday, and while I had the cover off I noticed the foam on the "temperature blend door" had turned to powder. I also found that the other door (ac/heater control) had lost it's hinge or pivot point. I can't see it but it just flops around. The vacuum control motor in the plenum works. How difficult is it to get at? Remove the whole dash? 1985 w/ac. Thanks!