Questions about a 5200 track ball

I just acquired my first 5200 track ball, and I have a few questions.

When using it, it bites my fingers if I get them near the edge. There is a small gap between the cover and the lower half of the ball. Is this normal?

You can see the gap towards the bottom of this photo.





Also, when rolling the ball, it is quite noisy (as if rolling the ball is generating some kind of friction). Is this normal?


The unit itself is unusual. I assumed it was a modded unit when I bought it (the seller didn't know), but after having a closer look at it, I am wondering if it may be something else?

S/N is "001045 EP 183".