I've just got one of these Alfine 8 hubs, on a used 2016 Ridgeback Flight 4.
The gears were slipping badly and freewheeling intermittently. I knew this when I bought the bike, the price reflected this.
Stripped the hub down to the internals and separated the internals. (Not very difficult.)
The bearings were worn badly and brown with rust.
The internal gear mechanism was coated in manufacturers white grease, but not a lot.
Degreased the internals with Carb cleaner and left it to dry.
Oiled the internals with gear box oil.
Coated the whole internals, inside and out, with lots of semi-fluid liquid grease.
Renewed the cone bearings and greased them with waterproof Marine grease.
Reassembled the hub etc, went out for a short ride, all 8 gears were working fine, so I went for a longer ride.
All 8 gears are working well up to now, time will tell.........