Needed: Help with rear diff lock on '85 4kq

[Jpinkowish at aol.com]

Hi folks,
The rear diff on my '85 4kq locks fine using the console switch.  However, 
when I switch it off, the diff stays locked.  The center diff locks/unlocks 
normally.

At the rear diff servo itself, I can use a Mityvac to pull a vacuum on the 
locking side(terminus of hose #18 on Bentley p34.32) and can lock the diff.  
Using the Mityvac to generate pressure, I can force the servo to unlock the 
diff.

When I switch to the other(unlocking) side(terminus of hose #17) of the 
servo, I can neither generate a vacuum to unlock nor generate a pressure to 
force the servo to lock the diff.

Before I go diving into the console/vacuum reservoir, etc.,
--does this indicate a bad servo?
--is further diagnosis necessary?

--anyone have a WORKING rear diff servo available for $$ or trade?  I have 
lots of 4kq bits/spares to trade.

Thanks.  Look forward to your replies.

Jan Pinkowish
'85 4ksq
Bristol, CT