Answer to: How to clean 8-way controller?The flex component should work well. Unfortunately, the previously suggested 60D 8-way controller does not work in the 6D - it is slightly smaller and the ZIF connector at the end is also different. I'll try ordering the flex component too. Fingers crossed.
Answer to: How to clean 8-way controller?If you follow this guide, you can take off the back panel. From here its relatively easy to access all of the buttons. You can remove the connection and screw (indicated by red on the above photo) to take out the 8-way controller. The plastic control dpad itself is simply clipped on to the electronics and can be removed by gently pulling back the clips (I used a very small flathead screwdriver). As you can see underneath was quite dirty, and cleaning it has helped somewhat but not completely. I will need to source a new 8-way controller despite the cleaning! :(