You can do just one axle, but chances are if boots are torn on both axles the one that isn't making noise now will begin to make noise soon. Unless there is evidence that the passenger one is newer than it's probably not far behind the other one in wearing out. Rebooting the one thats not making noise will buy you some time, but it could start making noise at anytime. And to reboot the axle you have to pull it out anyway. But axles don't come cheap so I understand the concern.

__________________