No, Really...If you've gotten the Heater box cover off... You're much more patient than I'll be in 6 or 7 re-incarnations. 'Job Well Done!
I Don't have any access to the W126 Chassis HVAC manual.
(Or ANY W126 Manuals)
I believe you're talking about one of the operating rods for the Vacuum Pods ?
[Gently, remove it from your work path]
Just for fun,inspect the engine compartment side of the FireWall(s?) to make
sure one of the Gnomes in Stuttgart didn't SECURE the rod on the other side
with a nut.
All the MB Vacuum Pods have got to be the same,same.
(Germans hate Non-Conformity,and standardization is kinda a religion over there)
they are kinda a Twist lock release design.
These are a couple of GSXR's AND SIXTO's Vacuum pod Tutorials for W124 they should be
generic enough to help you:
http://www.peachparts.com/shopforum/showthread.php?t=245697&highlight=Vacuum+pod
http://www.peachparts.com/shopforum/showthread.php?t=246382
And
http://www.peachparts.com/shopforum/showthread.php?t=35373&highlight=Vacuum+pod
http://www.w124performance.com/images/W124_dash/