Have a strange leak on my 190e's 5spd manual trans. It appears to be coming from the rear drivers side of the transmission (cleaned it off and watched it leak down the side) I don't think it is coming from the rear seal, instead it is either coming from the speedo cable hole (which has a cable installed right now), or it is coming from a little cover held on by a 10 to 12mm bolt. Anyone know what this cover is for? I know nothing about transmissions so I don't want to pull it off without know what it is. Leak is pretty bad, about a quart a week.

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1983 240D 4spd
1984 190E 5spd
1987 300D (sitting for a year or two)
1989 Toyota Camry 5spd (current DD)