Originally Posted by
cpach
I know you're joking but I'm a full-time professional mechanic. I've never once replaced pulleys on a personal bike. Most pulley replacements are from people who never check chain wear and end up with comically stretched chains, but I've also seen some very high mileage rides wear them out, usually after dozens of chains and multiple cassettes. I've also seen a few from running in very dirty conditions but in those cases the whole derailleur is often worn.
Yea, I don't think they're something that needs replaced often - as I''ve only had to replace deraileur pulleys twice in my life, once do to the rear wheel eating the rear deraileur (tried to salvage the pulleys, but no dice), and the other time was that they were just really worn from a lack of maintenance. As in tons of side-to-side play causing the chain to sometimes wedge between the cage & pulley.