It's not just the GSX vehicles are transparent: even your airplane is transparent! A problem with missing *parts* of vehicles/scenery objects, it’s a video driver or an FSX graphic setting problem (a tweak in the FSX.CFG which should’t be applied)
Try all the following:
- Update your video driver
- Reset your video driver settings to default
- Reset the FSX settings to default, by removing the following file:
%APPDATA%\Microsoft\FSX\FSX.CFG
This will force FSX to rebuild a new config with all default settings.