Your father is a wise man
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I would suggest starting by disconnecting both yellow lines to the left (as you are facing it) of the brake booster. Plug the lines that the yellow lines hook up to. Start the car and try shutting it off and see if it shuts off. If it does then your problem is a leaking door lock system. If that does not do it then you need to get a Mighty Vac and start putting a vacuum on each line to ascertain where the leak is at.