I recently swopped these switches on the steering wheel as they were not working correctly. The replacements I got from eBay were not much better!!
So with my original switches I dismantled them to get to the micro switches inside them and gave them several good sprays with contact cleaner.
To get at the microswitches you first have to have removed the unit from the steering wheel. From the back of the unit press the centre button to see the slides which you then need to gently prise open with a small screwdriver to release the button. Then the outer buttons can be removed by gently prising the supports that the button pivots on. A lot easier to understand what I mean when looking at the switches.
Re assemble in the opposite way ready to be re-installed