300 d wont shut off
 

My 300 D 1984 wont shut off with the key,
I checked all the lines and found the tee on the main vacume hose going to the brake booster may have been cracked, it has some type of silicone sealer on it and it also makes a hissing noise when I shut the ignition off

The only proper fix would be to replace the booster hose. It's cheaper than you might think, about $25 if I remember right.