The circuit board beneath is a completely different story, you'll probably need to do some cleaning here using some contact cleaner and a cloth. Another problem that occurs often is that the pod has worn a hole through the PCB track. If this has happened, then placing the pod with a slightly different orientation should solve the problem. Don't try to fix the hole with solder, because you'll raise the height of the track and the button won't work properly at all afterwards. When everything has been cleaned, use some new tape to hold each pod in it's correct position. The pods have 3 contact points and three straight sides. Make sure none of the contact points is are touching the track of the centre contact. When assembled correctly, one of the straight sides should bridge the track coming from the centre contact. You can test each pod with your finger before assembling the housing again.