To remove a pressed in barrel, use a heat gun to heat the valve body where the barrel inserts. The idea is to heat the valve body but no where near to the point of glowing or turning red. After just a minute of heating while holding the assembly firmly by the barrel and vertically smack the valve body with a rubber mallet or piece of wood. Be sure the valve body has a soft landing spot. That's all there is to it. After installing the barrel back into the valve body be sure to apply a small amount of JB Weld all the way around the barrel to valve body interface to seal the barrel.  Allow at least 24 hours for the JB weld to set.