Zero Turn Mowers

I have a new RZ4623 and the drive belt that powers the hydrostatic drive motors keeps jumping off the pulleys when I turn at slow speed. I asked this question in the Warranty section but I have not received a workable answer from the factory reps. I am an auto engineer so understand what is going on mechanically. I know the belt is not damaged nor or the pulleys damaged or misaligned. The only thing I can see is the spring that preloades the idler pulley is not putting enough tension on the belt to keep it from developing a wave and jumping off the pulleys. I tried to get the factory to send me a new spring but it looks like that will never happen. They want me to take it to the Lowes I bought it from, the one that left the seat interlock connecter unplugged and the pivot bolts out of the seat. Do any of you guys have any thoughts?