Before updating GSX to the latest version t all worked ok.
What do you mean with "updating GSX" ? Just Live Update ? If yes, if you missed one of the vehicle updates in the past, you are missing vehicles so, in order to be sure you have everything update, it's best if you also download and install the vehicle updates OR the latest full GSX installer.
However, your report was about missing PARTS of the vehicles. If you missed the vehicles, you wouldn't see the *whole* vehicle, not just parts of it. And this problem can ONLY be caused by a problem with video settings.
I cannot see how to reset the video driver settings to default.
In the video card control panel there's an option to restore setting to default. And, when you install a video driver, if you choose the option to do a "clean install", it will reset all video driver settings.
You can also try to reset the FSX settings to default, by removing the following file:
%APPDATA%\Microsoft\FSX\FSX.CFG
So FSX will recreate a new one with default settings.
After you restore your preferences, be sure you enable the HIGHMEMFIX=1 tweak in the Addon Manager, press "Save to FSX" and restart the sim.