you need to find out where the oil is coming from mate, maybe pics would help. black oil as said is usually not what you'd expect to see in a gearbox, could be engine oil if it hasnt had a change recently. if your concerned about the gearbox look in the area of the drain and fill plugs on the passenger side, and the very back of the box where the propshaft comes out - could be an oil seal. other than that the only place it could leak from are the silicone sealed joints in the box itself or at worst the input shaft oil seal and leaking into the bellhousing (doubtful)......if its an engine oil leak check the turbo oil feeds and returns, the area around the oil filter, around the sump and plug and down the front of the engine where the belts are as the oil pump cover silicone seal is prone to leaking. then come back and let us know
