Not sure about the OM601, but the shutoff on the OM602 and 603 is directly connected to the injection pump. Drivers side of the engine, under the manifold on the 601

Pictures on these links:
OM601 (2.2) http://www.peachparts.com/Wikka/OM601InjPumpOilLeak
OM602 (2.5 Turbo) http://www.peachparts.com/Wikka/OM602InjPumpFuelLeak

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1982 240D, sold 9/17/2008
1987 300D TurboW124.133 - 603.960, 722.317 - Smoke Silver Metallic / Medium Red (702/177), acquired 8/15/2009
262,715 and counting