Do you have broken keys on your keyboard? It's starting to get difficult to find replacement keyswitches at a reasonable price.
So, instead of lurking on eBay, and replacing the whole switch, just replace the broken plastic post. Available as singles for a quick repair, or sets of 12 if your keyboard is in really bad shape.
This part replaces the stem in an SMK "long stem" keyswitch, Apple part #s 705-0081, 705-0084, and 705-0082. See the images for more details, or the archived Apple documentation here: