Engine oil and coolant leaks are not overly common on the 6.7L Power Stroke diesel engine however they are not immune. With there being a lot of components taking up real estate on the top end of the engine finding leaks can be a challenge. The quick connect fittings used on the Garrett turbocharger for lube oil and coolant are becoming somewhat of a pattern failure.
Oil and coolant leaks that show up at the lower rear of the engine at the transmission converter housing more than likely originate up top. Both fittings are located at the top of the center housing of the turbo and a clear view of them is obstructed by the upper intake manifold. using a small mirror and a good light source may help you find leaks there or the use of a borescope may prove more effective. If there is any doubt remove the upper intake manifold to expose the turbocharger and to replace these fittings.
The quick connect fittings are the similar for the coolant and the oil.
Coolant leaks can be slow and will build up a lot of crust at the fitting.
Oil leaks will usually be more of a seep but close inspection will reveal the source.