I did this on my 69 Fury while transmission was in the car last year and wanted to offer a couple things for those struggling with this. Replacing the seal may not always be the cure, it might be the symptom. Sometimes those seals go bad not (only) because they age out but because the shaft pivot itself has some wear or other defects. This was the case (pun intended) with mine.
I replaced that shifter seal a couple times only to have it start leaking a year or so later. Motivated (po'd!), i dropped the pan and pulled the VB. Having the VB out of the car lets you really inspect that shaft and dress any snags, etc. This also makes removal and install a breeze with no special tools (see above bolt and washers basically). I found that the selector shaft in my car was grooved at the seal point and had some minor damage (probably from my own ham-fisted previous work). I thought that was it...
However, after putting it back together i noticed that the shaft seemed really loose in the seal. Pulling it back apart, i found the lower hole in the case that supports/contains the selector shaft pivot was egged out, allowing the upper shaft to move all around in the seal - not stay centered in the seal. At first i thought it was the rooster comb but upon inspection i found the damage to the case.
Note: This was a high mileage transmission originally from a 73 New Yorker (185k miles now) that was rebuilt about 30 years ago.
I found a Sonnax tool/jig that allowed me to drill out the lower hole and install a bushing to hold the shaft centered. Job done and it no longer leaks! (however that darn rear pivot/anchor o-ring is now leaking. Sometimes you just gotta pull and reseal these things... maybe! We'll see - maybe that's another sticky thread as it's gotta be the 2nd most common leak point.
)
PS - Alternatively, another shade tree way to do this seal (this thread) is to get a 90 degree drill (or dremel?) in there and put a hole in the case seal for a small screw. then install a screw that will either push the seal out (or grab the screw with a pliers and wriggle the seal out). I have only done this with the transmission on the bench and didn't want to drop pan (fresh fluid). I now have this seal puller / install tool - but this is zero buck sleezo way.
