i'm not a tig welder, but anything i have read up on concerning tig welding in general stresses cleanliness no matter the material being welded. stanton suggested to not clean the crack because it was a fresh break. that may be so, but the case surely is dirty [because of the skin porosity], and you would be welding to it. plus the case casting is not really a very high quality of casting is it ? i have a new tig outfit in it's box that someday i hope to learn to use, so i try to read up and learn as much as possible. i have also read you should be very careful when v-ing out a crack or beveling a joint in preparation for welding aluminum you should be careful to not contaminate [make dirty] the joint prep by using a disc, stone or cutter previously used on other material. is this true ? the thinking is the same as grinding your tungstens on a dedicated wheel.