well as long as you dont run dry your ok but it is kind of a pain. You do not need to split the case. just take the rside cover off. Take the shifter off and then remove the few phillips head bolts holding the cover on off. If you don't have an impact driver get one as the phillips head bolts are usually a pain to get loose with a screwdriver...especially a 74 thats probably not been apart in a long while.
Realistically you can replace this seal without taking it apart but its so easy to take that cover off I'd just take the cover off and push the seal out fromt he back...but if you really want to do it without removing the cover here is how you do it. take of the kick starter. drill 2 small holes. probably 1/16" holes, in the outer portion of the seal taking care not to knick the shaft or the outer case. Then screw in 2 sheetrock screws in the holes and using pliers of some sort pull the seal out. then pop the new seal in using an appropriat size socket as a driver.