Skoda 120L diff leak

Hi all

I'm new to the forum, having recently bought a 120L that I am trying to get back on the road. 

My car has a small amount of oil dripping from one of the swing axle boots. Can somebody please explain what seal needs to be replaced? My Haynes manual shows how to replace the boot, and the diff side cover gasket but makes no mention of an output shaft seal. I assume there is a seal in there, is it straightforward to replace without pulling the gearbox apart?

Cheers

Anto