One thought/question that I have is how tight is the bearing that fell out at this point? I ask because the welder may have heated up the case and caused it to expand, thus leading to the race falling out. In any case, figuring out how it should fit/feel and assessing how worn the case is in this area may be pretty easy as you can use the new case for comparison/measurements. There are ways to secure the race in the old case if it's worn and needs help but I agree that if it's out of spec that I'd use the new case as well since you have it.