On my '89 560SEC I noticed something that took me by surprise recently.
I had the passenger side valve cover off for inspection, and up from the depths of the intake manifold popped the stray end of a 3/16" plastic vacuum line
I found its home by feeling around the bottom side of the black rubber breather hose which extends from the valve cover to the underside of the air cleaner, again on the passenger side. The hose connects to a tube on the underside of the air cleaner.
You'll recognize it as the tube that extends horizontally and rearwardly from the bottom of the air cleaner. The hose connects by hand, which I have to fish around underneath the air cleaner to connect to the tube whenever I replace the air cleaner.
On the bottom of the hose at about its midpoint is a downward facing nipple that's hard to see. The vacuum line plugs into the nipple.
I would venture that many of these vacuum lines have been dislodged since they are small and easy to lose. It wasn't there when I bought the car used four years ago.
Anyone had a similar experience?