Luke: nice stack of dimes. I learned a thing or three watching a world class welder. It looks like good welding.
Smallerfreeze: you could be right, that though the valve is ugly, it might still work, but more to the point, that it failed before, you have no history of who did the work, the previous owner wants nothing to do with it and because of the pressures associated within the dump chamber itself, it failed once, it can fail again. If the valve was something ultra rare, ultra unique then it might be worth trying to repair it. But a minimag valve, even early on, is not uncommon, nor better or even worth more than a regular classic valve.
You have a good standing offer to not only replace a possible hazard, but at no cost to you (shipping washes out). We in the community would rather meep you alive, uninjured and shooting a mag. It may not be the one you purchased, but you will be able to enjoy it none the less. This is not any ill will towards your intelligence or experiences, but from everyone here, who has seen this is in total agreement to not even put air to it and see if or when it will fail.