Have 95 4x4 I6 with m5sd. I'm replacing clutch slave and while trans down removed top cover and even though the gears all look good they are covered with a black film like you would find in the bottom of an auto trans. When I pulled the drain plug magnet it was covered with more of the same material. Tranny runs and shifts fine but was wondering if this is normal. Also, I want to clean it out...what should I use?