The upper lip seal is on the input shaft where it goes into the upper gear box. You need to uncouple the engine, slide it back a bit, pop off the coupling and a metal ring protecting the seal. The seal size is 60-90-10.

One could put it on a long term preventive maintenance schedule (maybe 5000 hours?), or, frankly, if you can deal with working on something that is worn out, just wait for oil beginning to show on the "C" drive housing below the input shaft. Perhaps better yet, change it when you change your Vetus coupling internal rubber shocks.

Cheers, Craig SN#68 Sangaris