This can only be one of two things If it's coming from where you're showing.....
Gearbox output shaft seal failed OR final drive input seal failed.
Could be either to be honest. My advice, drop the final drive down, it's a 15 minute job, see if it's running down the swinging arm or not. That'll sort out where the leak is. If you're unsure, give me a PM. I can find out easy enough and I'm not far from you...
Roger...