Sniperx: I am assuming that there is enough clearance between the pushrod and i.d. of the hollow input shaft so that the limited vacuum simply draws from the clutch side. No vacuum is applied to the interior of the gear box. There is certainly enough gap for leaked gear oil in the cavity to make it to the clutch disc. Anyway it was just a thought not a recommendation.
You still have not made a case, at least to me, for not seating input shaft seal all the way in to the cavity. Steptoe ought to know and that is what he says that he does. Easy enough to make the pvc seating tool if you want to.
I'm fairly certain that I say an uncovered bearing from the cavity in my 2000 build date. That does not mean that yours is not covered. I don't see what difference that makes anyhow. I do not recall an groove cut in the cavity to oil the bearing such that driving the oil seal in too far would block it.
for sale: 1968 R 69 S-us original condition