Well, as an update, again thanks everyone for the suggestions.

Unfortunately, my vacuum leak was a complicated mess to fix.

I was convinced that the brake booster line was at fault. After ordering a new line and installing it in the dealership's parking lot with the cold wind howling, of course, it didn't work.

So, I again got my trusty vacuum pump and discovered that the leak was coming from the climate control. Fortunately, over the summer, knowing that these cars suffer from ruptured vacuum pods in the dashboard, I had ordered all of them but never had the time to install them.

I tackled the job this weekend in the garage by removing the entire dashboard and center console to replace all 6 of them. This is the first time that I have tacked this enormous job. In my opinion the climate control system is the most overengineered piece of garbage that Mercedes engineers ever devised, only matched by their clear arrogance by the placement of these garbage components that none of them would ever need to be changed.

The job was a mixed success. The car now shuts off immediately, and I now have heat coming from the floor (did not use to have heat from this source); however, it appears now that I have to troubleshoot why, with the rush of the blower motor, the rush of warm air is flowing from the defrost vent and faintly from the floor with nothing from the side vents. So, it appears that I will now have to go back into the dashboard and diagnose this gremlin. As I understand, it could be anything from jammed flaps to a monovalve to a cracked CCU unit.

__________________
Brian
'94 E420 - 99K
'12 C300 4 Matic

Previously owned:
'06 CLK 500K Cabriolet
'85 300SD (Old Smokey)
2002 Boxster
2002 C320 (The five-pointed star Mercedes)
1993 300E 3.2 (Dealership's cash cow)
1979 300SD (Chrome beauty)
1983 300D (Old faithful)
1983 240D (Right lane cruiser)
1977 240D (Miracle of bondo)