DELTA3

So I bought this 99 XJ a few months ago. It has always had a clunk from the drive shaft (bad U joint). It has gotten exponentially worse this last week. So I purchased some new joints, crawled under the jeep and yanked the shaft. The front joint was so bad that it wallowed out the yoke and made the whole oblong. So now I need that yoke that slides over the tail shaft of the transfer case (slip yoke).
I also noticed a very thin film of oil coming from the seem where the T-case bolts to the transmission. It was very metallic and gray in color. Almost like a bearing was eating itself.

I'm hoping I can replace the just the yoke and the T-case will be fine after a fluid change.
Any idea what that film of oil would be?