Can this be repaired with JB-Weld and a tubuler insert to bridge the outlet and the 3/8 inch that broke off under the clamp in the hose?
How old is the radiator? Replacement is a common need for older BMWs. I doubt repair is possible. Also, make sure your motor mounts are good, that the engine isn’t rocking back and forth.
www.radiators.com or 1-800-RADIATOr
Replace the radiator. A repair is not feasible or cost effective.