We have several (18) model 11304-034 demo hammers. Is there a way to sub parts from a 139? We do have to order armatures and brush holders for some of these units anyway so a change of more than the fan would not be a problem if it will work. We were given the direct number for Bosch and they said all we had to do was change the armature, but if you check the part number on these two units it is the same. I would appreciate a call if possible at 507-461-0758. Thanks