If it is a metal pulley, you can drive out the old bearing to replace it. You will have to read the number off the bearing itself, and type it directly into google for results. I can't remember the number, (6502 or 6205, etc) but it is a common bearing used for nearly all GM pulleys for many years. I had bought a dozen of them in case I had supply issues, but they are at the shop, and this is the weekend.