If your doing this replacment because your wiper arms go all over the place
(when they shouldnt), put a washer and lock nut on the shaft.The wiper
shafts are a tapered shaft(like ball joint shafts). You can remove the nut
and the arm will still stay attached to the shaft(try it).Prying the wiper
arm will over come the force(the taper shaft is small,after all) that
attached the arm, and it will come off.The nut presses the arm onto the
tapered shaft.

Basically, most of the attaching force for the wiper arm is in the taper
and splines.A washer and locknut adds clamping pressure to the end of the
shaft. Then you got good grip from the taper and end.Do this, and the
wiper arm will probably stop wandering. It will be in the right place when
the rain comes. Dont need new wiper arms.