My first guess would be where the moto message is.
Generally speaking, they had some bleed line issues with the moto message before switching to 1/4 inch pvc bend, they had this tiny bleedline nipples, which really serve no purpose.
My suggestion would be to drain out the tub, and clog that bleed line from inside the hot tub (need to take 3 screws off the cover plate of the moto to do it.) You can get a stint and some devcon from your local HSS dealer, or ask them to perform that service, which should be fairly inexpensive. $150-$250?
Before you go down that road... the spa wasn't drained for any length of time... especially over the winter was it?