Sounds like it needs replacing. You wouldneed to drain the oil first and make sure the surrounding area is free of oil, dirt and grit before installing a new seal.
Just make sure it definitely is leaking from there first.
It’s easy enough to do. Drain oil, remove casing from other side. Remove gearshift. Slid out gear shaft, clean. Remove/replace oil seal. Grease shaft and reassemble...
More or less...
Just done the one on my 3SH - when you put the new one in make sure that you cover the gear lever shaft with tape so it does not damage the seal when you push it through. Budget for a new clutch cover gasket and oil as well.
