When you wipe some of it off with a white rag, does it smudge red, or black?
That U joint looks suspicious, as it is also coated with the 'stuff'. So it could either be leaking from that seal (red tran fluid) or just some oil/grease coming out of the u joint (black stain).
It could also be that when filling some other fluid, it was spilled on the shaft and then got flung all over.
I guess I would clean up the area, check your trans fluid level, and then look for it again in a week. :smoke: