I bought an old SB 220 recently. It has a new capacitor bank and relay. Everything else looks like stock. After several weeks of use on CW, SSB and FT8 the tuning capacitor is starting to arc after it's been correctly tuned for the freq The cap had a lot of dust so I cleaned it and filed down the spots that were damaged. There were a couple of spots, but the majority of the plates were clean. The plates cannot be removed- they are pressed onto the rod. After re-installing, the cap still wants to arc Should I buy a new one or is there a modification to prevent the arcing?