I have a 1962 Longines cal 280 mechanical dress watch that was my father's. It has always ran well, but about a year ago I noticed it didn't hold a wind longer than about 12 hours. I sent it to a watchmaker specializing in mechanical movements for servicing. Upon inspecting it, he said it needed cleaning and oiling plus a new mainspring. He sourced a mainspring from his supplier, but advised me upon receiving it that it didn't look like the one he removed. He nevertheless installed the new MS and discovered that the spring slipped in the barrel, resulting in the inability to wind it more than about 10 winds before slipping. I was returned a cleaned and lubricated watch with a new mainspring that still won't hold a wind longer than about 12-13 hours.
I found the correct MS at cousins UK (GR 2673 T) and sent it along with the watch to the watchmaker, but upon seeing it he advised me it was the same MS he installed and returned both, suggesting I should leave well enough alone.
I am curious what others think about this. Is the GR 2673 T the correct MS? There is also a 2673 MS for a cal 280 listed on cousins with the suffix "non-automatic," but I have been advised my barrel requires the T end. If it is in fact the correct MS, how difficult is replacing it? Could the degree of difficulty have been why the watchmaker did not want to attempt installing the MS a second time? Finally, does anyone know of a watchmaker with Longines expertise who could replace the MS? I live in Seattle. Thanks.