Glass materials for patio cover

Glazing manufacturers have spent decades perfecting a spacer system that does not eventually leak and condense. They still haven't completely perfected it, though they are much better than 20 years ago. There is no way you're going to put together a system that does not eventually leak, especially with a vacuum. You'll have a better chance with inert gas, but I'm not convinced even professional argon filled glazing stays argon filled years later. It's not that I doubt your fabrication skills, it's just that it's a very difficult problem to address.

For all the time and effort spent assembling a window system, it's worth buying professionally built glazing units. If you want to save some money, forgo the argon filled and simply get dual glazed units with a low-E coating. IMO, these offer decent thermal performance and good value.

It would be best to wait for a couple of dry, sunny days before applying exterior sealant, but if you fear that rain will enter through the window edges it may be necessary to execute an emergency repair. If you have a 2-3 hour window of no rain in the forecast start the repair by removing only the sealant on the window edges that show the easiest routes into the house (lower horizontal edges?). The sealer will remove easier if you slice both edges with a razor knife. Coax the sealer off with a putty knife. Once removed apply (in order of best at sealing): 1) 100% silicone caulking, 2) window putty or glazing and 3) latex caulking. Use a caulk gun for all 3 suggestions. 100% silicone is hard to shape but seals the best. #2 and #3 are the easiest to work with; they seal sufficiently, but need at least 4-6 hours to become rain repellent (a hair dryer will shorten dry time).