That is my opinion also. One may be able to burn the oil out of the pores with a rosebud enough to stick weld it. I would think that the casting is cast steel rather than cast iron and is more easily welded. I have welded on rear axles with good results using E7018 rods but not over oil soaked material. You would have to get all the oil out and then heat it sufficiently to vaporize the oil leaving only the carbon residue in order to make any weld metal adhere. I would either try to fix it or replace the axle now rather than wait for it to fail under heavy load as this could create a dangerous roll over situation.If it's a porous casting and a crack that has resulted around it, brazing might work for now, but in my experience, the oil that has penetrated the metal and "infused" it will not allow for a good bond.