I'm trying to extract a corroded in diesel injector. Three out of the four came out by using a puller and slide hammer together. The fourth is more difficult. The threaded end has broken off the injector and so the only way to attach the puller is by welding. but the weld keep breaking every time I apply force with the puller. I always get a brittle fracture at the interface between injector and puller. I've tried MIG and MMA and it's the same. I've attached a couple of pictures. First one shows the puller to the side of the injector and the second has the puller fitted over the injector. What am I doing wrong?