I FOUND MY MK23!
IT HAS BEEN LOST SINCE LAST NOVEMBER!
Picked it up and squeezed the trigger.... thup, goes off without a hitch. TM mags are gastight for at least 9 months outdoors it appears.
Yeah I also have lots of Allen keys, but the bolt on the stock tube needs an abnormally long torx wrench to tighten.
It wouldn't be a bad gun if it came in a 2tone colour that wasn't vomit-worthy orange