The gearbox coupling should be fitted with 2 pressed steel flanges pushed on to the plain spigot - the inner one throws any leaking oil into the catch channel around the input shaft - the larger outer flange covers the outer lip on the front cover plate. There should not be a felt seal in the channel around the shaft - the seal is in the housing that is inboard of the coupling, and is only accessible from inside the 'box. My advice would be - don't worry about the oil loss when the gearbox has been stood on it's front end, it is designed to do that! In normal use, any oil that leaks past the input bearing, gets flung out into the catch channel and drains through a drilling to pass through the front layshaft bearing and back into the gearbox. This drilling also doubles as a breather for the gearbox - so when you stand the 'box on end, the oil returns up the drilling and on to the floor!
Regards,
Eddie.