The finishing touch to my gearbox rebuild was to add a flexible tube onto the top of the thrust oil filler. I have got so fed up with the awkwardness of trying to get oil into this out of sight filler. The hose will flex enough to avoid interfering with the clutch travel.
I got fed up of oiling the clutch thrust bearing and cleaned them out and pumped them about half full with grease about 20 years ago and not looked at them since.