Unless the driveshaft has been dinged or hit something, or you are experiencing a vibration problem, simply replacing the U Joints with quality replacement joints should not normally require the shaft to be rebalanced. I have replaced 100's of U Joints over the years, even ones with a center floater or ones with double Cardan joints and did not rebalance any of them and never had a issue with balance.
It is necessary to pay close attention and mark components before taking them apart and reassemble them in the same order/orientation they were before taking them apart. They came from the factory balanced, so just simply replacing the U Joints should not change or affect the balance if done correctly.
But if you want to spend the money to balance one, it certainly won't hurt anything, it's your money....
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Supporting Vendor and Moderator of LOST05 Jeep Liberty CRD Limited
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