I'm chasing vacuum leaks on an '83 300SD. Gray on gray, in case that matters; about 269k on the clock and I've had it for a year now. The shut-off is always a bit slow; and sometimes recently I have to manually press the stop lever under the hood.

I noticed oil leaking out of the start switch so I replaced the shutoff vacuum solenoid on the ip (not quite sure whether that was the source of the oil but I've heard it can be).

Usually on those occasions when the motor keeps running after the key is turned to the off position, I can get the motor to shut off by shifting into one of the lower forward gears (with foot on the brake). Does this indicate where I am losing vacuum? Is the modulator bad?