PCB, stands for power control board.
Actually its printed circuit board
Disconnect the negative battery terminal - you need to do this to avoid logging an airbag fault. Before doing this, be sure you have your radio PIN handy - you may or may not need it.
Remove the horn pad by inserting a large flat blade screwdriver into the holes on the back and twist to release the clips. Remove the horn pad carefully, disconnecting the airbag wiring connector and place the horn pad aside in a safe place, away from people and fragile objects (you never know!)
Disconnect the wiring connector for the steering wheel buttons and feed it through so the buttons are free to come out. There are a couple of screws holding the buttons - remove these and remove the controls from the car as a pair.
On your workbench (you DO have a workbench right?
) disassemble the buttons very carefully with a small jewellers flat blade screwdriver - the clips are visible on the outside of the buttons. Be CAREFUL - you dont want to break any of the plastic clips. Once you have these apart, you can access the PCB with the microswitches.
Using a proper electronics soldering iron with a fine tip (don't use a plumbers soldering iron) heat each of the solder pads until the solder melts - then apply a small amount of fresh solder (for electronics - flux core not acid core) and remove the iron from the joint. Do this to each joint in the unit.
Spray the microswitches with some electrical contact cleaner. (available at Jaycar - cat number NA1012 for $11.50 per can) Give them a fair soaking as you are relying on some of it running down into the switches where you can't reach. The contact cleaner evaporates very fast so while spraying, or immediately after, press the buttons quickly a few times to work the cleaner through.
Once you've re-touched the solder joints and cleaned the microswitch contacts, you can re-assemble the buttons and install everything back into the car.
Remember that you have nothing to lose by trying this - even if you completely wreck the buttons, you were probably about to go and buy another set anyway werent you?
Note - the electrical contact cleaner is a fantastic thing to have. It will fix a huge number of electrical problems not only in your car, but also at home. Personally I've used it to fix an intermittent power window switch problem, the steering wheel buttons, some noisy hifi connections, a hard drive intermittently losing power in my PC, and HEAPS more.
