Failure mode - Mercedes-Benz 3.0L V6 Diesel (Sprinter 2007-2022)

Oil cooler stack seal leak (the signature OM642 repair)

Reliability tier: aggregated - verify before ordering, see /disclosure/

Symptoms

engine oil level dropping between services with no visible pan drip
oil seeping where the cooler stack sits between the cylinder banks, tracking down the back of the engine
oil film on the transmission, subframe or getting onto the exhaust (smell/smoke)
low oil warnings on trips despite correct service fills

Compare with the other causes of the same sign on this engine: oil leak, oil consumption or rising oil level

Root cause

The OM642's oil-to-coolant cooler stack lives deep in the valley between the cylinder banks; its original seals harden with heat cycles and weep oil. The service consensus across independent Sprinter/Mercedes shops is that this is THE known OM642 oil leak: the original seals turn stiff while the updated seals stay pliable. NHTSA VOQ is effectively silent on it (owner complaints go to dealers as 'oil leak' without component detail) - the load-bearing evidence is the service literature, so this record is disclosure-graded like the LML VOQ-silent topics.

Diagnosis

confirm the leak source with UV dye or a degreased engine observation - rule out the valve covers and filter housing first
check coolant for oil sheen (a failing stack can pass oil into the coolant side)
check oil level and top up before the drive to the shop - the leak is slow but the level drops are real
on repair: replace the full seal set with the updated material, not just the worst one

Fixes

oil cooler stack reseal with updated seals (labor-heavy: the stack sits deep in the V; plan for intake and ancillary removal) ()

oil-cooler - more than one option: OM642 Oil Cooler Seal/Gasket (642-188-05-80, current), OM642 Oil Cooler Stack (642-180-01-65), OM642 Oil Filter Housing (642-180-14-10-64), OM642 Oil Filter Housing Gasket (642-184-00-80)

Prevalence

very-common