Nearly fifty years ago Airstream, Philips, and Corning met and conspired this window design. I'm not a forensic Philips-Corning scientist, and there must be greater authority, but as I have observed...
type 1... Very difficult to replace silicone bedded glass, leaked at top horizontal edges.
type 2.. Introduced the clamp-bar and tape bed, leaked at top edges(clamp-bar ends). Easier to replace glass.
1968 type 3... Improved clamp-bar, leaks less, stainless steel glass edging to enable deeper skull gouges and enhance appearance by hiding black window seals. The edging may protect glass from chips and aid in prevention of breakage.
The desperately needed types 4, 5... were never conceived.
All types leak through the long horizontal top hinge in wind-driven rain.
If you leave them open during a wind-storm, they'll blow away.
The foam tape deteriorates and windows fall out if not latched closed.
There is very little concurrence on how to restore these windows. There are pages and pages of posts with varying opinions. Everyone is trying to help.
The grey seals in your “stack” windows shrink with age. In a post somewhere, it is said that similar seals are available at a hardware store. Your stacks appear to be siliconed from the outside, so they probably don't leak. If they are not leaking, “back burner” them and move on to more important areas. Maybe razor trim the outside sealant off the glass for now.
Where the jamb meets the sill, there is sealant. Leaks here won't be known until the floor below rots.
RTV Room Temperature Vulcanizing. Unfriendly to most aluminum. There is an aluminum friendly silicone, but there are very few silicone applications on an Airstream. Clear polyurethane sealant may be superior.
The word "calk" can be used as a verb.
For sealants, everyone has preferences. My choices for sealants are Trempro 635, Acryl-R, and Captain Tolley creeping crack cure. I keep a tube of Parbond on board for emergency leaks, but have had none. Acryl-R in a blunt IV needle syringe kicks ass.
Dig out the old sealant with whatever you have that doesn't scratch the aluminum.
Coming to terms with the balance of cleverness and foolishness you'll find while restoring an Airstream is part of the romance. Keep it fun for you... Every answer is most likely found in previous posts. Google search is superior to Forum search.
1968 is the last year of the “old fashioned” twinkie tailed, narrow body, lightweight, wood interior trailer. They never got better...