I have a perfectly good tub not being used because of leaky jets, so I want to permantly seal them and use the tub as a soaking tub.

I have a perfectly good tub not being used because of leaky jets, so i want to permantly seal them and use the tub as a soaking tub.
Try unthreading the nozzle and use a threaded PVC plug that fits the thread pattern and screw the cap in place of the jet nozzle. Use Teflon Tape on the threads. Your local plumbing store should have the PVC plugs, Good luck. Tom

If Tom's solution doesn't work, my son, who has a pool and spa company, uses thin Fiberglass discs that they epoxy to the inside of the shell.

While the advice given is great you are going to do so much work it may be just easier to repair the leaks since both solution would have you remove the existing jets.