As I previously posted to this question in another forum:
"Nope, I have never seen an 870 Express stock MIM extractor fail, and issues relating to the carrier dog follower spring are rare. However, I always upgrade both because the cost and time involved in doing so are minimal (the spring costs about $4 and the extractor about $12). Interestingly, Remington charges the same for either carrier dog follower spring, so you have to wonder why they just don't use the heavier spring (used in the Police) in the Express. The answer, of course, is marketing. BTW, I also always upgrade the magazine spring to a heavy-duty Wolff spring ($8.99)."