I've just checked the GSX download link, and it works normally, download starts immediately and it's very fast (considering the server it's in the US and I'm not).
In any case, the update can't have caused GSX to disappear, unless you *ignored* the main 1.3 update, and applied the minor Update. In this case, it should be enough to download and install the Stand-Alone Addon Manager, possibly after a Windows reboot.