Sounds Like a Vacuum Pump Diaphragm Replacement
Just my .03 worth. Been there done that sort of thing. If no vacuum is available for braking or his locking or shut off valve, I'd look to see if the exhaust line from the vacuum pump isn't sucking engine oil to the filter housing. A definite sign that the diaphragm in the pump has a hole in it. Diaphragm can be ordered from parts shop for a minimal amount of green, don't purchase a new pump when the old one can be rebuilt easily.