I've posted about an oil-leak before, but I'm not sure anymore if its the oil cooler. The entire block, it seems, along with the oil pan and various other parts of the undercarriage are just caked in oil. Its black and nasty, and there even oil making its way into the air cleaner from the air recycler thing that comes out of the valve cover. Any ideas about whats going on?

Gotta clean it up to find the leak. Oil lines that feed the oil cooler are possible culprit, same as the oil separator pipe that ends at the sump. What car is this? Turbos can have other possibilities. And you've been nursing an oil leak for how long?

85 300Dt, been leaking since i got it so at least 2 months.....it sat for about 6 months. Whats the best way to clean that mess up?

You are probably going to need to wash it several times. Cheapest way I know of is to get a gallon of Gunk Concentrate and mix with 2 gallons of kerosene. With engine warm but not hot spray this on the engine and let sit overnight. Spray off with hot water if you have it available. Let dry before repeating... but repeat until clean. Then start up and test drive short distances and look for the leak.
Not sure about your air recycler deal... if you have oil going to the inside of the air cleaner from a line then you may have a vacuum pump diaphram leaking... which should be addressed sooner rather than later if true. Good info in the archives....