I just checked my 74 Argosy and the slider windows don't appear to use the plastic track insert. I then checked Peanut which is a 77 Argosy and didn't see the plastic slider either. Plus I have a slider from a 78 Argosy that doesn't have the plastic slider. So it would appear that all of the Argosy line did not use the plastic slider insert.
However, I don't think Airstream changed the window frames and I wouldn't be surprised if the seal and slider components from the later models could be retrofitted into the Argosies.
I have a windows from an 86 345 that I can use to compare the frame construction to my Argosy. I'll try and do a compare in the next week or so. It would be nice to know there are alternatives for repairing these windows.
Air forums # 1674
1974 20' Argosy Motor Home
1974 31' Excella trailer (parting out, as of 4/1/2015 I have wheels, brake drums, windows & holding tanks left to sell)