Leaking Oil Drain Plug

I have a 85 500SEL. I changed the oil, and the drain plug is leaking oil. It's tightened to specs. I did not replace the copper gasket with a new one.
Could this be the problem. Should I re-drain the oil and replace the gasket with a new oil drain plug for safe measure. The leak is not bad, but irritating since the engine does not leak at all, but now it has one possibly due to me not putting a new gasket on. Opinions please?
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replace the copper washer. copper is soft (relatively), and is meant to act as a malleable seal there.
?
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DERR..

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