The 1/4" with 6" extension and a 10mm swivel socket worked on my 91 300d 2.5 Turbo. I got mine at the local Sears.

Don't be surprised when you get a white, ceramic (I think) shutoff valve from MB; it does fit in place of the original metal one. The vacuum line nipple is on the top rather than the side, but you can just use a longer piece of tube --it clears OK.

While I was picking up the part, an MB mechanic wandered over and warned me (see above postings) of the danger of "run-on" ; he suggested removing the intake manifold and standing by with a suitably-sized piece of plywood with which to cut off the air sucked in should run-on occur. Sounds better than cutting fuel lines.

Mmm, sure is nice to stop with the key...