Tough to tell from the pic, but it looks like the plate directly below PTO shaft has fluid on the top of it. Could be coming from a bad seal in the plate, or down from the PTO shaft. You'll likely have to drain all the fluid before you pull the plate, or the PTO shaft to check the seal(s).
I would think it would be an easier fix to replace the gasket around the flat plate below PTO shaft.
Keep us posted.