I have had to put new o rings on the kegs, and pressure relief valves, and poppets for inside the posts.
I just reconditioned 6 kegs for just under $100, it's the first time in 10 years I did "major" work to them.
No more going online for parts and waiting for them to ship either, now that home brewing has become more poplar there is most likely a specialty shop right around the corner that will sell you parts.