Fuel line shut-off valve if operating correctly should stop fuel from entering engine crankcase while engine is setting idle IE not operating BUT valve will have no affect on the problem while engine is operating. In today's world of "almost right parts" I would be checking transfer pump to determine if it was the cause of fuel in crankcase. Another option is just disconnecting fuel transfer pump & installing an electric fuel in it's place. If it wasn't the cause then R&R umbrella seals on inj pump shaft. You definitely don't want engine oil thinned by diesel destroying your engines crankshaft bearings!!!!!!!!!