Glock just announced that it has initiated a voluntary exchange program for recoil springs on Gen4 Glocks that shipped since August 2009. Glock has been been modifying the recoil spring assembly since the Gen4s were introduced, and it's announcing the voluntary exchange "to standardize the [recoil spring assembly] to gain the best possible performance in each pistol...The new [recoil spring assembly] compensates for all design modifications made to the Gen4 and allows the pistols to function up to Glock's rigid quality standards and reliability goals."
Glock Gen4 G26 and G27 models, which we reviewed in our October/November 2011 issue, will not require the modified recoil spring.
You don't have to return your Glock to the factory or take it to a gunsmith to replace the spring. Just fieldstrip the pistol and install the new spring. Call 877-745-8523 to order a new spring. For more details, visit Glock's website.