I've been using borrowed PC but i now have my own PC up and running with access to hex edit software. I've had a look at the GVN53 firmware and unfortunately it doesn't have the required txt commands in it for ldr.bin to execute 'rrgn' or any other such commands to dump or overwrite regions. What's even worse is neither does the Edge 500 firmware, so we cannot use SD that way at all.

Could you please look again at the XML file presently on the unit? I want to be sure that the software version is still showing as 300 since you tried to update with WebUpdater. Put the V3.30 gupdate.gcd back into the Garmin folder and power the unit on, then connect in MSM to check the version number.