That can be tig welded, but the prep would take a lot more time than the welding.
The case half would need to be removed, degreased and blasted to do it right.
It might be possible to degrease and clean area with a small Burr and weld with just the tank and other parts removed from the case. Going over the area with the arc first can burn out the oil and debris, then it can be wirebrushed and welded.
I'd personally just JB weld it muhself, and I can Tig Magnesium.
Plus, anyone that owns an AC tig is gonna charge you $50 minimum. The filler rods are $2-3 each. I'd charge you beer Mikey.