First, the KSFO installer takes the bglmanx.dll exactly from the *same* location of our installers. In fact, it's even more unlikely you would end up with a corrupted download using our installers, since we have the URL duplicated on two mirrors (which are also chosen at random each time), while the KSFO installer use only one of them so, it's should be exactly the opposite: if you had a problem with the internet connection, it should happen more frequently with the KSFO installer.
In any case, if you still have connection problems, or you have another product blocking the download, like an antivirus or a firewall, you can simply fix it by installing the Stand-Alone Addon Manager with the network disconnected.
Your other problem, of missing parts of buildings, doesn't have anything to do with the Addon Manager, and are due because you are either running FSX in XP Compatibility mode, or you have a wrong setting in your FSX.CFG
In the first case, turn off any compatibility modes for FSX.EXE. If that doesn't fix it, remove the FSX.CFG and let FSX create a new one from scratch. The file is located at %APPDATA%\Microsoft\FSX
