You'll need to replace the vaccum shut off valve. The diaphram is probably leaking which is allowing engine oil from the injector pump the enter the vaccum system.

You need to replace the valve to help shut down the engine and to stop further contamination of the vaccum system.

Remove the panel under the drivers side of the dash board and look at the vaccum element on the ignition switch, it'll probably be covered in oil.

Check that the vaccum pump isn't leaking oil (you should have a clear vaccum hose on it anyway).

Install a filter (A 000 078 06 56) between the main vaccum line off the vaccum pump and the first fitting leading to the the interior vaccum. This will help prevent oil from making it's way into the brake booster and damaging it due to oil perishing the diaphram.

Unfortunatly there's already oil in your vaccum system.......you may have future problems.