Years ago I fitted a rubber oilseal at the front of the gearbox (in the bell housing end). It leaked terribly and soaked the clutch. I seem to remember that I solved the problem by fitting a NOS leather seal from Nolans in Peckham.{anyone remember them?)
What is the state of play today with these? Are they still leather?
Can’t comment on the seal but fondly remember Nolan’s . Gerry Nolan was a real character. Happy daze!
They are rubber today, pretty standard technology with all transmissions. If yours leaked there must have been something else wrong. If you are going to do it again, post some pictures of your input shaft. Maybe there is wear or a scratch or something.