I feel like with mine, when it can't start because it's too cold, and I end up cranking a lot, then the oil gets washed off the cylinder walls with diesel or other sprays (starting spray, or carb cleaner?) then the rings probably seal even less making it really hard to start. That's just a theory though.

Is yours cranking fast?

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1987 300E

I've been jumping battery, spins fairly fast. Going to try genuine starting fluid tomorrow.

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1984 MB 300SD Turbo