Concur with Jim...
I replaced the nylon inserts on the thumbpiece (cylinder release) on a couple of Colt Pythons. Also replaced & fitted a hammer on a Python (someone bobbed it). I've also fitted a new hand in an older Colt (pre-Python lockwork). Fitted a bolt (cylinder stop) on an older Colt Official Police too. Now with exception of the Pythons, these were older guns that had seen hard service.
On S&W, I've replaced several cylinder stop springs. I've fitted a sear or two. Stretched a couple of yokes to remove the endshake too. Replaced the hammer on an old M-15 (ex-LAPD gun) to restore the DA feature. Replaced some rear sight blades (one half of the adjustable sight broke off on a couple of them due to neglect).
Overall, revolvers require less parts replacement than semis. Modern semi-automatic pistols tend to use roll pins and everytime you pop one out, you use a new one. The springs tend to be more fragile too. On revolvers, you tend to have coil springs (or on the Python, one big leaf spring). On pistols, there's quite a number of tiny elbow springs (trigger bar spring on some, hammer reset, trigger spring) that can be "tweaked" if careless.