You said that the protector doesn't fit like it used to, so this indicates that the gimbal may have been subjected to mechanical stress at some point. Stress on the shafts can damage the pots.
It's possible to look at the pot, but it's a very delicate operation. First you remove the 3 screws from the back of the roll servo and remove the cover. You'll see the pot as the D-shaped component. You'll have to very carefully pry off the black cover to see the "track" of the pot. This is the delicate part, since you don't want to damage the cover or any nearby components.
See the picture in this post for what I'm talking about:
http://www.phantompilots.com/thread...zy-p2v-camera-gimbal.20514/page-7#post-277348
In that picture, you'll see a crack in the pot's track. You'll also see the tweezers I used to pry off the cover, and a 4x magnifier to help examine small parts. There's other useful info in that thread.
See this post for some more replacement info:
http://www.phantompilots.com/threads/gimbal-chicken-dance-most-common-reason-and-repair.36509