from what i have read about this procedure around here- and i hve read a lot- there seems to be a gret deal of prying the old hardened seal out, possibly damaging something like DD suggested, but maybe your dad's idea will help fill any voids your screwdriver may have made?
I'm sorry i can't be very helpful, but I am about to replace my shift shaft seal (when the mf arrives) and wanted to ask you to post your solution when, and it is when not if around here, you get to the bottom of whats happening, as the urge to just ride away on your nicely sealed moto may override your desire to type in how yu did it. and i am posting so that when you do find it, the solution will pop into my unread replies, hopefully around the time the freaking seal decides to get here.
so 'scuse the less than helpful post
-KK