I will agree that the tip provided for lubing the wiper will help. but maybe only for a while.. Ive seen customers with the same problem and I have lubed it up.. and have never seen them again. and other times they are back in a week or 2 with a completley siezed wiper!!
luck of the draw I guess!!

and for everyone wondering why the dealer wants to sell you everything.. (the motor, linkage and gearing).. its becasue the gearing or possibly linkage is seizing up causing extra load on the motor.. slowing everything down when it hits the middle spot.
so If you just replace the motor, you have fixed a third of the problem.. and you will be back with another seized or slow wiper. so they say replace it all so the problem doenst return, a costly repair......but needed.