The sealant is window urethane sealant. You can get it at any decent glass shop. The newer stuff usually will set-up more like windshield sealant, not stay all gooey like the factory stuff. It does, however, seal better.
I resealed mine, as they were letting water in and caused a little rust on the rockers. When I had the rust cut out and repaired, I pulled the glass and resealed it.
Ryan