I bought a "parts car" '79 300SD and it runs so good I am still driving 3 1/2 years later. I have no idea what kind of oil was used for the first 160,000 miles, but I started to use Castrol Syntec 5W50 40,000 miles ago. The leaks it had stopped and it now uses about 1 quart of oil in 10,000 miles instead of the 3 quarts it used when I first got it. I also use a small amount of PTFE so all the improvement may not be to the synthetic oil.

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