Hi Richard,
I stumbled upon your post searching for my BSOD issue and besides having an Arg1 of 19 in lieu of your clients 18, my details are exactly the same.
I read Vir Gnarus suggests "to remove the graphics card, clean up any foreign material that may be in the slot, and then reinsert it, as well as update graphics drivers if they haven't already."
I'm currently downloading the latest drivers for my GEForce 570, and will clean up any foreign material that may be in the slot when the pc is shutdown, but I'm wondering if this rectified the BSOD issue for your client?
Cheers
Graham