is your transmission a manual then it would be gear oil.If automatic the clutch have graphite in them and cause the black,nothing to worry.Tramission should fluid should be change every 40,000 miles.I use Mobil One ATF and change every 80,000 miles.

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1999 w140, quit voting to old, and to old to fight, a god damned veteran, deutschland deutschland uber alles uber alles in der welt