Originally Posted by Squiggle Dog

This is just a theory on my part, but I wonder if the Dieselmeken pump is bad and dumping fuel into the crankcase, which then fills up into the head and comes in through the valves and hydrolocks the cylinders.

This happened on my roommate's 1991 W126 350SDL after doing a diesel purge. It cleaned out coagulated vegetable oil from the injection pump and what was left were badly worn and scored walls and pistons which dumped fuel into the crankcase to the point of stopping the engine.

Or, the Dieselmeken pump might also have something wrong with one of the pump elements, so it may be stuck open and constantly pouring in fuel to one cylinder when running.

I'm guessing there is an issue with the injection pump. They are a reputable company, but mistakes happen. This is just my guess based on a similar experience.

As for the crankcase filling up with fuel due to a bad injection pump theory, you could confirm this by checking the dipstick tube and finding it near overflowing, or draining out way too much thinned down engine oil that smells like fuel.