Had this on my 2011 Zetec S, bought some new buttons and swapped out, all ok now

i bought my 2015 fiesta a year ago. since the day i got it the buttons play up. Mostly it is the up vol button. it does nothing. If I want to increase the volume I have to press the down volume and then release it, this seems to then enable the up button to work when i press it. Bit annoying but not annoying enough for me to be bothered to do anything about it. . as pressing the down vol prompts the up vol to work I think it may not be the button itself.  I think (not sure) that the buttons are all linked to the radio by one wire (not a separate wire for each button as that would be impractical for the number of swivel connections needed to the steering wheel) and the radio knows which button you press as each button has a difference resistance . so maybe the radio is not good at recognising the resistance value for the up button for some other reason. I don't really know, guessing a bit. 

Or have I totally misunderstood how the steering wheel buttons communicate with the radio. Can anyone say?     (I much preferred the radio controls just below the indicator switch on my mk6.5 fiesta and mk1 focus.)

Mine went back a couple of years ago and I was told it was replaced, then it played up again and ford said there is nothing wrong with it. Does anyone know the cause? Could it be just a build up of muck under the contacts? Could a clean with alcohol fix it?