If you want to waste one, take it apart. That way you can see what the problem is. Getting them back tight may require some glue. They are so cheap I would just replace them unless a squirt of cleaner helps. You can get conductive plastic TKD faders for around $40.
All those opamps mentioned are single package parts, don't mix them up with 5532's, OPA2134's which are duals. A good new part to sub a 5532 that has similar bandwidth is the AD8599 from Analog Devices. It's very low noise (1 nv) and low THD. Surface mount only so you need an Aries or Brown Dog header. This one is pretty much a drop in for the 5532 like the Analog Devices OP275 but better. Get 'um all from Digi-Key, 1-800-digikey or
Digi-Key Corporation - USA Home Page
Jim Williams
Audio Upgrades