Vibrate motor not working except for alarm

I recently replaced the aluminum housing on my iPhone 5s, following two videos and the iFixit guide, and made sure to bring back most of the insulation, all of the metal parts from the original/dented up housing. When I turned it on, I noticed my vibrate motor stopped working. I thought it stopped altogether, but today I learned that it still works because my alarm rung and vibrated.

EDIT: I have done a DFU restore, and now my phone vibrates /sometimes/ as I'm tinkering with various sound > vibrate settings for text messages, ringtones, mail, etc. I can't seem to get the vibrate to work when I turn my phone off silent, but when it is on silent and the vibrate feature is on, it vibrates.

EDIT 2: I now notice that the vibrate gets progressively weaker the more I turn on and off vibrate functions in settings. Perhaps the motor is simply getting old/needs to be replaced? Do vibrate motors hold a charge or something from the battery?