What type of bag is this for? Generally, the gussets are the sides of a bag*. The gussets help to decrease or increase the volume of the inside of a bag (often via tightening or loosening a bag’s sangles). I’m guessing that your Spa invoice is suggesting that some of the stitching on the gusset(s) of your bag needs to be redone.
As far as the touret clasp, I agree with the other member. Maybe it’s too loose? Maybe there is an internal issue with it? I don’t see any reason to replace the other gold plated areas of your bag unless:
A) Your bag is from the early 1980s or before.
or
B) Your bag’s hardware is very scratched/tarnished.
Whatever you decide, I’m wishing your bag a nice, relaxing Spa.
*For example, gussets are present on Kelly, Birkin, Constance, HAC, Sac à Dépêche, Kelly Dépêche, Jerboise, etc.