I believe I have a vacuum problem but not quite sure. Car will be operating fine but when I apply my brakes to stop there is no booster assist. And if I go to turn the ignition off it continues to run and I have to manually kill the engine by depressing the stop lever in engine compartment. Let the car sit for a brief period and upon restarting it will operate normally. I can drive the car when it is acting up and after a few miles it will start behaving normally. Am I on the right track? If not what is it?

You are on the right track!

Diesels--since they have constantly wide-open throttle and hence no vacuum--require a vacuum pump to provide vacuum for things like power brake boost and various solenoids including, it appears, fuel shutoff.

http://dieselgiant.com/mercedesvacuumtroubleshooting.htm

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Kent Christensen
Albuquerque
'07 GL320CDI, '10 CL550. '01 Porsche Boxster
Two BMW motorcycles