A large percentage of leaks come from failed seals and gaskets on the shell.  This may be hard to check if the hot tub is full of water, and much easier if the hot tub is empty, but it’s certainly worth checking out. 

Tips:

–Check around every hole that’s been drilled through the shell  (jets, floor drain, light lenses, filter chamber, intake screens, underwater valves, etc.).
-Poke with the tip of a screwdriver or nail, check for gummy, crumbling gaskets
-Check for silicone or epoxy smears which indicate an amateur attempt to stop or slow the leaks seeping through the shell.