I have a LA SPA Quest 8500 hot tub in my backyard (inherited from previous homeowner). It has a 60AMP GFCI box connected on the outside of the house which is then connected to a 60AMP breaker on the main in the basement. My 60 AMP GFCI oustide occasionally trips. I don't think there is anything wrong with my tub as I've had it attended to by local spa companies. But, I do think that my breaker has just gone bad with time. I am finding however that 60 AMP GFCI breakers are very difficult to find. I've noticed that many hot tub companies are selling 50 AMP GFCI with their tubs. Is it possible to put a replacement 50 AMP GFCI outside which would then be connected to the existing 60 AMP Breaker in the house and still run the hot tub? Any input is appreciated. Thanks!

You can physically make the switch, it will fit. However, you need to know the amp requirements of your spa. If the manuafacturer used a 60 amp I'm going to guess they couldn't get away with a 50 amp, or they would have. You might not find the 60 at your hardware store but I'd order a 60 on line before thrying to make a switch.

If 50 Amp GFI is Ok for Yours, I would change inside with 50 Amp 2 pole Breaker.
Even if you have it "attended", corrosion in motor can leak to ground, causing ground fault.
If Motor can be unplugged or disconnected safely and easily. See if breaker trips. If it doesn't , bad motor, if it does, try blower, etc...