Riding Lawn Mowers

am working on a Husqvqrna Model #l021H48F and the transaxle jerks and makes a noise when under load, the shaft that the pulley mounts to moves up and down roughly 1/4 inch, I need to know what would fix this problem and or what the price of a replacement transaxle would cost or should i just tell my customer that this equipment is junk since it is 8 years old. He has asked me to investigate this problem snd advise accordingly, this unit is very well kept and i would hope that this problem can be remedied with minimal cost. What do you suggest?