Good questions. Did you smell the gear oil from within the bell housing? If so then the front input seal may be leaking or it could be oil transported from the slave cavity.
Yours had the earlier grey colored input shaft rear seal so its good that you are replacing w/brown one. Did you use the drill and slide hammer method for removal?
No advantage to pulling the push rod just to replace that seal. I left push rod alone for fear of damaging it. Design is for it to come out the front.
Not convinced of the value of the felt. I think that you'd have to r-r the gear box to drill it. No body has tried this yet as far as I know but I've proposed that if the box was pulled then connect the kanister purge solenoid to the cavity via a trap. That would keep dust and moisture out.
Since the slave is usually good for 50k I don't worry much about providing for the drain.
Did you try my posted method of pulling the slave with banjo's still attached?
for sale: 1968 R 69 S-us original condition