Here's my hunch:

A tech who was in charge of disposing of a damaged engine is now attempting to sell it to some unsuspecting buyer. Among the various things to be damaged by using biodiesel, the turbo would be among the last.

In theory, if the turbine was oil lubricated and substantial contamination of the engine oil occured (due to WVO use) , then the turbo could experience bearing failure.

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Vehicles Owned:
1983 Mercedes Benz 300D ~ 212,000 miles
2005 Mazda 3 S ~ 96,000 miles