Ttissot was founded in Le Locle in 1853 and joined the Omega family in 1930. Tissot used to be seen as a more down market cousin of Omega. Both brands are, of course, now part of the Swatch Group, As it is the movement, dial etc that needs service, I guess that the Omega service faciiity would do it. Possible that they might still have a replacement Omega case available to make it a complete Omega?