Yesterday I removed my wiper arms from my LATE '99 F350 so I could clean them up and re-paint them.
I had asked last week for info on how to do this and received several responses that were spot on as to how to do it-THANKS!!
When I started doing the removal I slid the latch part away from the shaft area, and gently pulled up on the arm and they both came off very easily.
I immeadiatly (sp) realized that the shafts were much bigger that any previous truck or car that I had ever removed before.
I think this is why the arms came off so easily.
Now for the question and observation: Has anyone else removed their arms and noticed on the back side the groove with either a very hard rubber or soft metal key in there?? (one of mine was missing) I'm thinking I should replace the key if I can find one or 2??
AND it seems rather you have the key or not the arms only will go on 1 way and can't really be "adjusted" like other trucks and cars can, which is ok by me as mine seem to be right in the perfect spot already.
NEXT OBSERVATION: While in the area I noticed that the plastic grille on the cowl on my drivers side (mind you my windsheild has been replaced by the PO) has a kind of clip thing in the middle on the edge closest to the windsheild that appears to be sticking up/out and doesn't look right to me...can anyone tell me how this thing should be installed/attached.THANKS!! & sorry for the long post!

 

Are yours splined shafts? Mine have an indention and splines, but not key.. Is it like a woodruff key? What kind of adjustment are you looking for? Like adjusting angle with respect to the park position? I can just put mine on at any angle as long as the splines match. I believe the pass side cowl molding goes one first, and the drivers slides into the pass groove...

 

Mine ARE splined shafts, very fine splines, I tried to put the arms back on and when I did I met resistance and so I turned the arms a little until they went on-mine apparently only go on 1 way.....I would think the woodruf key would hold everything together better, there IS a groove in the wiper are for the key, and 1 in the shaft as well to line up with.
My truck is a LATE '99 F350...may be the earlier trucks have the keyed splines and the later ones don't??

 

Mine are splined and keyed, but like you said, the key prevents any "re-alignment" of arm rotation. Neither of my wiper arms have the key any longer, and when I remove/re-install them, I just go through a few minutes of trial-and-error until I get them where I want them. No big deal.

Therefore, you really do not need the woodruff key. Yes, it makes the positioning "singular" in that they can only go in one position. However, the key does not do anything else for you, really, in terms of making the arm more secure. Since the shaft heads are splined, it is the combination of the splines and the spring-loaded latch that slides into position underneath the shaft head that holds the wipers in place both rotationally and vertically. The only purpose for the key is rotational positioning.

Regarding the clip you're talking about and the cowl covers. The covers are held in place with 6 screws each, IIRC. The covers are in two pieces... driver side, and passenger side, meeting in the middle. I cannot remember what the clip is for... perhaps related to the windshield washer hose routing, I think. Regardless, you should not have to do anything with it and can leave it as is.

Hope this helps.

Background.... I recently just got through having to replace the entire wiper arm linkage assembley and motor (now one piece design), and consequently have torn the entire system down and put it back together several times due to a broken linkage component on the new assembley which was not discovered until installation was complete. It's all still fresh in my memory right now.