I recently bought this old Longines in a thrift shop, but I have looked and looked for an identification and cannot find one. Perhaps if I knew how to get into the watch without damage, that would help. The caseback reads " use 1300 wrench". The dial of this watch is black with white dots covering the bottom two thirds of it's surface. They seem to be original since they are so uniform and well dispersed. There is a diamond (?) chip in a triangle at the 12 0'clock position. If you can help me, I surely would appreciate it!