I am guessing here... but if the vacuum loss is at the brake booster... there should be some one way valves in the system to where if the system is really pulling 20 inches you should only have one problem... the booster ... it is not easy to find the pictures and proper valves to get it back to original... but some have managed to do it.... the combo of oil in lines and booster not boosting and shutoff problems almost always indicates vac pump diaphram problems...