I just wanted to add something here. I found this thread extremely helpful, but… I did the fix first and it not fix the sticky key issue. I then replaced the whole locking mechanism. This still did not fix. I then started inspecting the key cylinder itself and noticed the wafers were not retracting 100%. A couple would stick out just a “hair”. I purchased a new cylinder and had a locksmith match the new cylinder to my existing keys (I did not want multiple keys). This fixed my issue. The symptom was identical to that described in this thread but another cause is possible. When you have things apart check the cylinder and make sure all the wafers retract completely just to be sure.