The spacer should have a dryer built into it to absorb any moisture the may be between the panes, or may find its way in. Use windshield adhesive/sealer to seal the panes. This used in the automotive industry to glue/seal the windshield to the body, to become a structural part of the body. This urethane is what you want to use to seal the windows, and it has a 6 month shelf life. The date is printed on the bottom of the tube. Using Silicone would be a big mistake, as it will not hold up long, and it cannot be removed readily. This advice is worth what you have paid for it, but learn from others that have done this sort of repairs before, and had failures using other types sealers.