944 CV Joints
CV joints can go quite a long way without any sort of problem. They generally fail in two ways: they wear out or the boot gets damaged and dirt is caught in the grease which then leads to abrasive destruction of the balls and the journals.
Here is a broken cage, this happened during a wheel bearing change because I allowed the weight of the disconnected axle shaft to overstress the CV.
There are essentially two ways to deal with a faulty CV. One, you can remove and replace just the defective joint (there are a total of four) or you can replace one or both of the axle shafts (sometimes referred to as a "half shaft"). The second method is more common and assuming you are getting a rebuilt half shaft that is rebuilt with NEW CVs; then this is probably the way to go. Why? Well, opening up a CV is first, a messy job. The moly grease softens the skin and cuts to your fingers and hands seem to happen more readily. The CV is a bit if a mental challenge too to get it back together. Avoid that part of the job if at all possible. If you have to replace a single joint though it is pretty easy because you can take the old joint apart and install a new one - no re-assembly of the old joint is needed. Above you can see I have disassembled the CV and am removing a snap ring.
With the ring out of the way I can use a puller to separate the CV "knuckle."