wtb: hvac vacuum servo

[treed2@u.washington.edu (treed2@u.washington.edu)]

So I verified where the hissing coming from my dash was coming from
today (it only happens on the 'upper vents' settings - not defrost or
'feet').. my defrost flap vacuum servo is apparently leaking. The vacuum
line to it is good, so I'm assuming servo failure is the only possiblity.
I haven't pulled the servo yet (it looks like a total pain in the ass -
I can't even see how its attached), so..

Can these be easily disassembled and rebuilt? I mean, is there any 
more to these than just a rubber diaphagm and a pull-rod? Like a valve
that could be clogged with deteriorating foam giblets or something..?

I'm gonna assume thats a 'no', so does anyone have one of these for sale
relatively cheap? Prices at the local yard are rather unpredictable so I
hate going there because I don't know whether the owner will ask for $5 or
$80.

Thanks

-Toby