[DutchmenSport]

Considering the support itself is not broken and it's just the flange, or flair, or whatever that's called that rusted and giving way, I think I'd take a different approach. First, the process of rewelding will be tricky to ensure nothing catches fire under there. I would think that would be a bigger risk than just leaving the broking "wing" as is.

I think a much simpler and safer solution would be to simply remove the bolts and slip a sheet of sheet metal, maybe 1/4 or less inch thick, between the bottom of the slide and the top of the slide frame and do not disturb the existing wing. Of course, you'll need to drill holes in the new sheet metal for the bolts to go through. Doing this will give the wide support again, and that won't affect the original part of the frame. (and no danger of fire attempting to weld.)

I think, if it were mine, I'd also clean wire brush out as much of the rust as you can and with a liquid weld, paste that over the existing metal and let it bond. After it dries real will, give it shot of black spray paint so the color matches and to help prevent future rust.

Well, that's my idea anyway, but maybe something you did not consider. I'm a firm believer in trying the least evasive action first before dismantling unnecessarily. If it doesn't then, then you can always try the next level of complexity, hot welding.

Good luck.