I agree that just re-soldering will probably last a very long time. After all, most of the s100's out there never fail in this way. Too many do -- especially when one of them is mine. I think that on those that failed the original soldering was not q...
When you disassemble enough to free the shutter release assembly (which includes removing GPS unit) you will pull a flex with a lot of fingers from a push connector. Removal is easy, but re-inserting is tricky because the flex (how shall I put this) ...
Someone who repairs cell phones might have the right iron for the job. The flex strip is part of the shutter release assembly. Replacing it does not require soldering, but does involve a lot of disassembly/reassembly. See earlier posts on this, and ...