I keep meeting Mercedes Sprinter owners who fail to break-in their Sprinter properly (the fault of Mercedes using inappropriate oil* for break-in), who change the oil far to infrequently (naively following the service interval).
And... some who have fueled up with biodiesel B20 or worse, covered in detail in:
Biodiesel should not be confused with renewable diesel, which is a far higher quality product, arguably better than petroleum diesel, albeit with dubious lubrication properties due to its ultra ultra low sulfur content (~5 ppm vs 15 ppm for ULSD), which in theory could result in fuel pump failur due to inadequate lubrication from the low sulfur content.
* Using 5W 30 oil will not break in a diesel engine properly because the piston rings will not seat properly into the cylinders, the oil being too “thin” (low viscosity). So you get 1% or 2% better fuel mileage for a few thousand miles when new, but the engine now has leaky piston rings forever. Thus it leaks fuel into crankcase oil (“fuel accretion”), particularly during a DPF burnoff cycle, which dilutes the crankcase oil and damages its lubrication properties. Over time, the engine suffers increasingly premature wear, which results in shortened lifespan along with reduced fuel economy over its usable lifetime. Mercedes won’t tell you any of this, which is awful, but regulatory bodies hold all the cards and call the shots, so Mercedes isn’t going to fess up on any of it.