Personally I would never run a hot tub w/o a GFI. The amount of current that is leaking can be very small, medium or high depending on the issue. A small leak of current w/o a GFI protection is probably not too much of an issue (damage wise to the tub), but a medium or high current leak could cause further damage to a component IMHO. Anytime I had a GFI issue it was always solved by methodically removing loads and running the tub on the GFI, as others have suggested. Over 33 years I have had 3 GFI issues. Twice was the heater, once was a motor that had a slight intermittent current leak. The motor was the one that was hard to figure. The fault would only show up every couple of days. So it became important to run with each component removed form service for days before the culprit showed itself.