[Tiara Open] 1989 3100 Open Wiper Arm Removal

[cp4000]

    So this is what mine was like...(See attachment)
it had splines, not knurled.  If you look close you can see a dimple which held in a washer which held in the C clip.  The C clip would move out of the way when attached and then snap into a groove when seated.  You can't see the C clip when installed.  Technically, prying it off, the C clip should release however, they are on so tight that I usually damage the washer and the C clip falls out.  
Does that all makes sense?