This is what worked for me thanks to post from Alegria:
wget http://downloads.openwrt.org/releases/17.01.5/targets/ar71xx/generic/lede-17.01.5-ar71xx-generic-tl-mr30
40-v2-squashfs-factory.bin -O /tmp/lede.bin
Got an error:
mtd -r write /tmp/lede.bin linux
Could not open mtd device: linux
Can't open device for writing!
Then this worked like a charm:
mtd -r write /tmp/lede.bin firmware
Unlocking firmware ...
Writing from /tmp/lede.bin to firmware ...
Rebooting ...
Now I am really thinking how to utilise my reclaimed Mark V.