That is your fork leg, or lower leg, or slider.
The forktube is the shiny one, that looks like... well a piece of tubing..
You can TIG it, be VERY clean, probably egg a bit, but seal will still work. They are cast aluminum. If they are all gouged, might not be worth doing. Unless you can get it welded cheap, and it is in otherwise good shape, it may not be worth fixing. check it for wear to the tube.
Seals are rubber over metal, some cheap types of seal are less coated on the outsides, CR seals come to mind.