Shifter shaft is possible, it is not trapped in the cases like the main shaft. You should be able to screw something like a drywall screw into the seal and pull it out, a bit of heat by pouring boiling water on the seal and surrounding case area helps a lot. The tricky part is sliding the new seal over the spline without damaging the sealing lip. You have to cover the spline section with something smooth like scotch tape, with a bit of a "point" at the end to ease the seal onto. This makes the shaft larger so use as little tape as possible. The shaft and spline must be super clean for the tape to stick. Oil the tape and shaft and the seal and carefully slide the seal on making sure the seal lip doesn't flip over. Once it's on its hole and level you use a stack of sockets or a piece of PVC pipe to gently tap in down into place.
