Sounds like more info is needed.Also, from my experience- it is more likely that the cable itself isn't pulling the lever away from the switch than it is to have a failed switch. Or it could be totally unrelated...

Why go back to bark?? I have started repotting the "chids I have had in s/h for 3-4 years as they do eventually have a sludge at the bottom from the algae that will grow in the translucent pots in good light. This seems to eventually have the same effect as decaying bark media suffocating the roots (just takes a little longer). I shake most of the old prime agra off the roots but do not pull off ones that are firmly attached---just spray gently with the hose over a collander to catch the loose rocks. Don't see why you couldn't keep the same size pot if you were willing to hack off some of the old growth. Be sure to spray the places that you cut with alcohol or hydrogen peroxide and treat with cinnamon to help prevent rot. Also be sure not to water for a few days after the repotting to try to avoid rot. I do the repotting in rotation with some new prime agra to start the first few pots. Those get the new media as the old media from those pots is being soaked in bleach and water in a 1/5 ratio for a day, and then rinsed several times with fresh water, and then soaked in epsom salts at a couple T. per gallon for a day. Then a couple of fresh water rinses for another day. (Something about the epsom salts releasing the built up minerals/salts in the prime agra, I read somewhere. (Most likely at the aforementioned very good site or one of his comments somewhere.) seems there is a tub of one or two of theese stages always sitting there. PLEASE jump in and give any suggestions or corrections to my methods here!

Ignoring the ground wires(since you know where they go) I can't be any clearer than this. You have two terminals(the part where you push the wire in next to the screw terminal is the same terminal, maybe that is your sticking point?) on the old switch. Let's call them line and load. The line terminal is the one with the 'mystery' wire. The load terminal is the other one. Take All the wires on the load side, marrette them to the load Side wire on your new device. Take the wire from the other terminal, marrette it to the other wire on the new device. Ta-da!

The white in a switch loop gets marked as black at the switch. When you open up the light box the black will be the feed to the fixture, and the white tied to the other blacks is pretty self evident as NOT being a neutral. If you open up the switch box it is also pretty clear what is going on with the black tape on the white as a reminder it is a hot. Neutrals are not switched anyway.