If oil is dripping out of the exhaust gasket, then it is still comming out of the inner oil seal and entering the turbine (exhaust) housing then leaking out. Does your truck smoke with an oil smell? Some times that can be tuff to tell on a diesel as they all do sort of smoke. Id clean the whole area around the turbo off and then run it and check for where the leak is originating from.
Pressurized oil enters the turbo frot the top via an oil line, and exits on the bottom via larger return tube. Its easy to see if the top is leaking, but still clean it and check anyway.
The bottom is harder, but I have had leaks before underneath that were hard to track down that ended up being the return tube. Lay underneath the truck with a good light and check it that way as you cant see anything from the top. Make sure the pipe isnt crushed or something like that. They usually have 2 small bolts you can snug up, but I wouldnt tighten them too much as you can easily strip them or break them off. If it is leaking there, and tightening it doesnt help, then a new gasket is in order which would be cheap, but a major pain in the ass to change. If you do id clean the old surface off with a razor blade and make my own out of gasket paper, or even RTV silicone will work if you dont have any other choice. I like to put the silicone on and tighten the bolts on the flange just a tad until the silicone begins to squeese out, then leave it and do a final tighten in half an hour or so when it firms up. I would inspect the down pipe closely as if it is clogged up or not free flowing you can pool oil in the turbo center section and it will leak as the oil seals are not designed to hold back pressure.
Also, you could disconnect your exhaust down pipe, and if oil is dripping there then I would say it would be most likely you turbo seal on the exhaust side. Cource you could also be having major blow by and your enigne could be an oil burner, but you would have a cloud of smoke behind you everywhere you went if that were the case.
Oil can also leak from the compressor side, but that would be unlikely as it wouldnt drip out of the back easily. It is easy to check as you disconnect the air tube that goes from the turbo to the intake manifold and inspect it for oil. Not like a film, which is very common, but lots of drips or soaking wet in some cases. Most intake pipes have oil in them to some degree and are rarely perfectly clean.
