Remember, a diesel engine runs on oil, however thin diesel fuel is, it's still oil. If motor oil finds its way into combustion it's just more fuel. Agreed, oil is about $5.00 per gallon fuel, but it's just fuel.
Try some frequent, hot oil changes. If that doesn't work, you may have to soak the rings with solvent. If you resort to this, make sure you never try to start the engine with liquid in the cylinders.
'84 Euro 240D, 523K miles
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