Wiper Assembly

I have been having the wipers slipping on the wiper hub. It appears the hub splines are stripped. I tightened the nut more than a few times, And I mean tight! The wiper arm still slips on the hub. Lots of ice and snow here so if there is any build up or resistance the wiper arm gets all out of whack. Sooo... I bought a wiper motor assembly from a junkyard and it was stripped. Returned it. Bought a part from Parts.com but it was not the whole assembly. Just the wiper hubs and light metal pieces which are easy enough to put on except for the light metal piece that attaches to the actual motor. It appears to be a rivet under a white cap. Is there some way to attach this part I bought? I did not take the old one apart as I am afraid I will not be able to get the new one on.

Never mind, it was a ball end , not a rivet. Twisted old off, rubber mallet the new on (with block of wood to support the assembly).