the hairline crack should be welded again with the right heat treatment to the aluminium...
my bike came with an öhlins shock as i picked it up. the shock in your bike looks like an wp aftermarket shock or is just taken from another bike.
the stock shock looks completly diferent ...
older suzukis and hondas used similar shocks . u should compare the length and diameters of the mountings... most shocks could be modfied to the right length in the case, that its longer as needed...
so i think , first you should find out, which kind of shock is in your bike and let it rebuild ..
with buying another used shock, it could be, that you might have a 2nd shock that needs rebuild..