Taking it apart will more than likely destroy it and proove nothing.
A good clean with contact cleaner while running the switch back and forth might just do the job.
As far as the switch operation, cannot see it properly in the photos you provided.
Does look like a 2 pole unit though and if one looks closely as it is operated, one can actually see how it contacts from a central bar, through the contact arm to the outer rim contacts.
As for the actual circuit of what it switches to where, you would need to meter that out (or visual in this instance) and draw an appropriate diagram.
Below is an example of different rotary switches.........