My earpiece seemed to not work as well. I could hardly hear anyone, which became very problematic as I work at home and attend many meetings via phone. I got to the point I had to use the speaker. Even with the accessibility hearing aids turned on, it was very hard to hear.
The repair went very well. I loved ifixit's packaging. It was extremely professional. I really enjoyed the repair guide. It was very well done. However i enjoy watching videos and didn't find one attAched to the guide (I didn't look very hard) so I used a PHONEDOCTORS video. Anyways, after the repair I still found the earpiece wasn't working well still which meant it had to be the earpiece grill was to dirty--it couldn't have been my repair job cause I'm awesome. So I ended up blowing it out with air compressor, vacuuming it out with a shop vac, and using duct tape to get in the crevice real good. I did each several times to make sure I got it all and viola it worked!
Try other non evasive options before you go replacing parts. It's not always mechanical.