Hi. Search the forum. All Line 6 button mechanisms are garbage. Helix is less horrendous than other products.
The black dust is from the foam. Helix Floor has more foam than the LT, as a result it is more susceptible to this issue. I have a theory that with time this foam becomes more tacky and less flaky, so the problem goes away after a couple years.
I cleaned tactile switches with liquid DeoxIT, and it lasted for 2.5 years. After that I had to do it again—this time I did it without taking the Helix apart (not recommended)!!. I angled the Helix so that the buttons would be perpendicular to the floor, added a generous amount of contact cleaner and let it drip down each button: about 4 applications. Then I waited for 2 hours, then pressed each button, and then vacuumed each button to get the excess contact cleaner out. I kept wiping the contact cleaner off the buttons and kept vacuuming until they were dry. It fixed the issue. Most people will say that it’s a crazy thing to do, but I did not feel like taking my LT apart again. And guess what? All buttons are as smooth as butter once again. I’m using my LT regularly since 2019 and everything works 100%
Use the liquid contact cleaner because it leaves no mess. It’s nonconductive, so it cannot damage anything. At most it can attract dust if you really flood the pcb with it.
I’ve fixed my Helix LT and Pod Go.
Below is my video for the Pod Go. On Helix, you need to take it apart, which you have already done.