I wouldn't open that rheostat. I have read that those heavy tabs are very fragile as Charlie suggested and you run the risk of snapping them. I did the best I could by cleaning from the rear opening with vinegar and a swab, rotating the wiper frequently as I cleaned. Worked for me.this might be a stupid question...I took the knob off but how do I remove the circular coil with a brass wiper? thanks again
The contacts, on the other hand (in the vented box), can only be cleaned properly by opening that box, again, being very careful with the tabs and watching where everything goes. Not only were the contacts tarnished, but dried grease and dust added to the problem.
Just my opinion, but I avoid using steel wool for cleaning inside switches. A strand left behind can cause shorts if you're not careful.