Fixed the clicking HVAC servo. In my case, the clicker was the top one inboard, which controls where the air comes out (dash, floor, defrost, etc.). This part is identified by Toyota as SERVO SUB-ASSY, DAMPER (FOR MODE) (p/n 87106-35120) and is available online for ~$142. I determined it to be the problem using the screwdriver method; after removing the glovebox for access, I took a long screwdriver and held it to the bottom servo - heard nothing. Moved it to the top servo and click click click.
Being a cheap bastard, I decided to try to repair it before buying a new part.
This excellent thread by [MENTION=113703]46runner[/MENTION] (thanks!) was my guide. However, I deviated from it in a way that worked for me but I wouldn't necessarily recommend to others b/c I may have been very, very lucky not to really muck things up.
After disassembly per that thread, I was able to easily get two of the three bracket screws out. If you're looking at the bracket straight on, the one on the left (toward the cabin) and the one at top right (toward the engine). The second one (toward the engine) is a challenge. I ended up using a long, flexible drill extension with a Phillips bit, turning it by hand.
The one at bottom right is buried behind everything and I couldn't think of a good way to get it even using the idea of drilling a hole in the side of the housing that holds the cabin filter. I did indeed drill such a hole but it was to remove the bottom screw holding the servo to the bracket. After taking out all three such screws (the others are pretty easy to reach), I was able to flex the bracket out enough to remove the servo while leaving the bracket in place.
I opened up the servo, breaking a couple of the clips of course, and did the usual repair process of cleaning the accumulated grease gobs off the three metal "fingers" and gently bending them up to ensure solid contact. I also carefully removed any gobs of grease on the contact surface.
The tough part as 46runner notes is getting the servo back in and engaging the three pins it has to move when it rotates. I eventually got it done after several tries, removing it in between to sort out where the issue was. And here's why I don't recommend leaving the bracket in place: the pins on the arms seem pretty solid but if you break one off trying to wrangle the servo back into place, you're probably screwed. I had to carefully move the bottom pin with long needlenose pliers to get it where it would land in the "trough" on the back of the servo.
Finally got it all together with the pins engaged, screwed down a couple of fasteners to keep it tight during the test, turned on the key and...nothing.
$#%$&#, what now? Oh, I forgot the electrical plug. :doh: Plugged it in, worked through the vent positions, and was very happy that the airflow went where it was supposed to go with not a click to be heard.
Patched the hole I drilled with metal dryer duct tape (very useful stuff!), completed the reassembly, and moved on to installing
these Auxito LED side marker bulbs since one of the old ones was out. They're nice and bright so the side markers don't look like an afterthought anymore.