You don't need the "foot switch assembly" for the Helix. That's just the hardware that makes mechanical contact between the external spring loaded plunger, and the top of the electrical switch soldered to the PCB. If you are having intermittent contact problems with one of the Helix footswitches, the problem is with the 6mm tact switch. You have two choices, both involve disassembly of the unit and removing lots of screws. There are some YouTube videos of other guys doing this. It may be helpful to watch them first.
Once you have the Helix footswitch PCB disconnected and flipped over to expose the micro switches, you can either try working a small drop of DeOxit 5 spray cleaner around the button and into the switch body (being careful not to spray anything else), or you can just replace the switch. Cleaning it usually works for a while, but sooner or later it will act up again. If you know how to solder, and you already have it disassembled, you might as well replace the switch.
The Line 6 Helix Floor footswitch is the same part many of their other products use. It is part number 24-31-1105 and can be purchased at fullcompass.com for $2.95 each, or from amprepairparts.com for 99 cents each. Their part number is TS-5127. The switch is deceptively small, but I can confirm that it works since I've replaced mine already with no problems. These momentary contact switches are nothing special. They are commonly found in keyboards and other devices made by various manufacturers. Do yourself a favor and keep a handful of them around in case they are all backordered later when you need one.
