If the main installer fails, you can sometimes manually install specific drivers by navigating to the Drivers/Apple/ folder within the USB and running the specific .msi files (e.g., BootCamp.msi ) with administrative privileges.
Apple occasionally hosts legacy driver packages on their official support site. You can search for "Boot Camp Support Software 4.0.4033" on Apple’s Download page. Look for a .dmg file named: BootCamp4.0.4033.dmg . If available, the SHA1 checksum should be verifiable. Bootcamp 4.0.4033 Download
