so this is the 'update' file:
rrgn,41,1:/Garmin/41.bin
reboot

there is no 41.bin file....

however, i did check g7towin again:
software version: 7.3
id: 1113
unit id: 3828582182
usb comm via bulk pipe

i did try your sd card method a 2nd time:
shows on my laptop as successful, and closes when i say 'ok' - but gps doesnt reset just keeps software loading message...