That cover is a RF Shield and Dust/dirt cover. You can't access the pot from the frame area behind the Dial Face, as it's a solid sheet. Even if you loosened the shaft of the pot, you'd still have to remove the cover.
The pot is just like all the rest of them in that it has a slot in the casing where the contacts go thru.
To gain access you must remove the shield/cover. Very small drill to drill out the rivet. Once you get it all cleaned out and finished, reassemble using a sheetmetal screw.
Larry