This is the first major thing gone wrong with this car. :( Does anyone know what could have caused this? How does something like this break? How is something like this fixed or is it better to get a new one? Or used rather?

Any advice would be welcomed.

Just guessing, but could've a u-joint popped and caused the shaft to break?? Fatigue, or age could be another factor. Go to used auto parts lot and get one off old vette that hes been wrecked. Old u-joints were the type that were not greaseable. Engineers expected them to last forever...NOT!!

Did the half shaft break or the stub shaft? If the stub shaft broke then order a new one. DO NOT get a used stub shaft! The splines and the ends of the stub shaft get worn and mushroomed. I would pull the rearend and check the internals to make sure no metal or chunks cause the breakage of the stub shaft. I would also recommend putting in a good synth rearend oil. By using this, you won't have to worry about using the posi additive.

If the halfshaft U-joints broke, then replace both sides and add new U-joint straps to hold the joint inplace in the yoke. Get good quality performance U-joints to replace the stockers. The ones without the grease zerks are stronger that the ones with zerks. Use synth grease inside of the new u-joints. I like to use marine grease because it repells water and is water proof and has a higher wear and pressure protection.

Good luck......:)