After the engine shuts off, how long does the stop lever stay down - minutes, hours, days?

Hook up the Mityvac to the shutoff actuator at the IP. See if it'll hold 20" Hg and for how long. If it'll hold indefinitely, hook up the Mityvac to where the brown lines attaches to the vacuum supply line. Go easy on the nipple or you'll have to replace the brake booster vacuum line. See if the system will hold 20" Hg and for how long.

Sixto
83 300SD