One of my bikes has a SRAM Rival setup. 2 years ago the right shifter broke. Based on some recommendations here I installed a Campy Veloce shifter and that worked beautifully. This season, I started having issues with the thumb shifter not returning to normal position after pressing. Its gotten worse and now about half my shifts get stuck. Is this purely the return spring in the shifter, or is the cable and derailleur involved?