Marvel mystery oil gets my vote for stuck pistons and rings,take out the injectors and pour a 1/4cup in each cylinder.Let it sit a week or so if it gets so you can turn it with a wrench be sure to cover the injector holes with rags and spin the engine with the starter before you put the injectors back in. Don

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Red Green "This is only temporary,Unless it works!"

97 E300D 157000 miles
87 300TD ?141k? miles