If you have a Glock in regular use (thousands of rounds shot through it) there are two things you should consider replacing. 1. In the older guns the recoil guide rod assembly. I think they run less than $10. The plastic guide rod system is a weaker point in the design. 2. Magazine Springs. Wolff makes replacement packs of 3 for less than $20. Notice the theme; it’s the springs. They are a wear item on the gun and for the minimal cost, you can make sure you maintain the pistol in good working order. These are also items any one can replace at home.
Right now I am working on a service pistol for an LEO. Gun is great shape but it was time to think about new sights, springs, cleaning the gun and he added the MCC extended control kit (one of my personal favorite mods ** Gen 1-3 only). Incidentally this is a really affordable service to get your Glock back in great shape.