Yea man sorry to say it but it comes down to liability. I would weld it up and shoot it if it was mine but wouldn't touch it with a 10ft pole being someone elses.
I weld...I weld some pretty intricate stuff....I wouldn’t weld that. If welded, and welded correctly, it would then have to go through a heat treat process that could warp it beyond tolerance limits....
Sarco has new/old slides every now and then. IIRC the mark II HiPowers were serialed in the frontstrap, right? Point being, not on the slide, too...replacement slide would be the way to go, then destroy that one....