Axle shafts wear out and break. Same goes for pinions and sway bars. Every time you accelerate the axle shafts twist a little like a torsion bar. After doing that thousands of times the metal fatigues. Especially if used off-road because they twist even more. If you upgrade to a 14 bolt axle it would be less stress on the shafts. But if those are original longs then they are probably like 10 years old. I'd say u got your money out of them.