Directional Control Valve (NCV3)
The OM651 engine has a 'smart' oil pump with a solenoid that reduces pressure to 2 bar under 2K RPM, and keeps it at 5 bar above 2K RPM.
Many Sprinter-Source forum users are finding that in the high-load situations the Sprinter is used in can cause a spring in the solenoid to stick open. Unfortunately, this can cause a severe low oil pressure problem. It's recommended that this solenoid is preventatively replaced at around 75k miles.