[KTL]

The old joints are pretty durable. I have seen some 20+ year old joints that still look good and can be re-greased along with new boots. But I suspect when you take them apart, you'll may find a pit in grooves where the ball bearings ride. The pitting occurs because the grease degrades with time and you end up with metal-to-metal contact.

Typically the most economical thing to do is buy a complete remanufactured axle(s). When you buy individual joints and boots, the collective cost is usually the same or more than a complete remanufactured axle.