Those bosses are only soldered in. What you describe is not uncommon by any means. I had it happen once when I was 2,500 miles from home. I had to drop the sump to change the oil, then drove home and fixed it.
Resoldering is not so easy now that it is soaked in oil but not impossible. That will only leave you where you were before - a weak joint. I recommend brazing it or welding and yes, the sump has to come off - not that it is a big job.