[lincpimp]

Is there a downside to sealing it up? I cannot think of any reason to not seal it up, and the lack or debris will add to the gears lifespan.

While a direct drive may not require lubrication, it will extend the life of the gears... And lube usually keeps stuff cooler, which is always good.

Access to the center diff may be more difficult, but once you have it set correctly it is not really necessary to get to it.

You would not consider running the ring/pinion without lubrication...