It would be easier in a way to just replace the whole sight but they can run anywhere from $60-$100 and there's no guarantee that it will fit. S&W lists 3 or 4 different sight blade heights that vary depending on barrel length and probably caliber as well, so the chances of getting a satisfactory match aren't too great. The replacement parts from Midway cost me about $15 so I'm willing to try and fix it myself. If I can't fix it I can then buy a replacement. I kind of enjoy the challenge of figuring out how to fix my own guns and I derive some satisfaction from doing it myself. I don't own or use precision tools (lathes, mills) and I don't consider myself a "gunsmith" by any means--I'm more of a "parts-replacer." Besides, I like saving money!
The S&W rear sight parts are very complex to manufacture but in terms of assembly/disassembly it's not too hard to do, except for that lock spring I've mentioned. What appears to be the elevation screw is actually a nut. There's a tiny plunger and spring that fits in the nut and provides the "clicks." The nut is held in place in the sight body by the lock spring. The nut then screws onto the threaded elevation post which fits into a slot machined into the topstrap.