My brother recently bought a 8320 (used, so no warranties at all), phone actually worked fine for a time, but since a week ago it won't click, I opened the trackball and notice a little dommed piece lose, when set back in place it "clicks" fine, so the question would be, if I buy a new trackball for his phone, will this solve this issue?
No, it won't solve the problem as it is not the trackball causing the issue. You posted the solution to your own query. Replace the trackball dome that you "set back in place".
Additionally, there is an 'audible click' setting for the trackball.
Go
Options>screen keyboard>audible roll
True. Except it does not make clicking the trackball audible, nor does it even remotely help rupalazzi with his problem.
The only thing that "Audible Roll" does is exactly what it says it does. The "click" you hear from pressing on the trackball is caused by the popper of the trackball dome.
If you were CONUS rupalazzi, I would send you one as I have a bunch of them. It's just a little sticker.