Hi Theo.
The aluminium is difficult to weld, possibly due to copper/zinc content. Also fairly poor casting , with voids and slag in it. Try preheat, low melting aluminum , stitching, and be happy with bead over the top , not full penetration , if you can weld it. V ing out a crack is likely to cause further cracking from shrinkage as it cools. Welding on external surfaces and areas where there is no problem with expansion /contraction not too bad, like replacing baffles, and motor mount lugs , welding on face of cases is very difficult, don't unless absolutely necessary , ie the case is unuseable as is.
Will try to find code for aluminum rod our guy uses tomorrow.
