I have the same issue right now. This phone have near a year of use.
I just noticed sometimes the vibration just vibrating in some other frequency. Not regular. Now it is like sliding.

I just dissasembled this phone one time ago just for curiosity and noticed that yes there are a vibrator in a place near metal shields. But I don't think it is easy to replace but I think we can use some glue in order to stick the piece. But anyway I don't think that is an easy work.
The vibrator is very little and it is in a small space.
The unbalanced piece (what makes the vibration) is very little and is like the same size as the axis of the motor. So we cannot simply use a clamp to fit it newly. But we can try.

Just when I had my phone dissasembled I was thinking that the vibrator just can fail. Because it did not seem robust enought.

Bad for now, it is just failing. And more bad: I'm in travel and here don't have tools to repair it. So I must use it damaged as is.

But the good news are that: What if you get damaged another part of the phone because it vibrates? Really this phone support so strong vibrations? The camera lens supports the vibrations?

I prefer not to use vibration for that. Instead I prefer a more weak vibration. It is possible? How? How to modify the motor for that? Can we use another motor or it is software controlled speed?

Here are a image of PCB where the vibrator is (marked in red).