I'm now on to my 3rd Open Face kit for my Tour -X as the foam piece that covers the microphone never stays on for longer than 3 months. It appears to stretch over time and never regains it's shape.
i either sew it in place (only a couple of stitches needed) to stop it moving or use a tiny cable tie.
or give up / leave it alone and cope with it as is.
still works fine - a wee bit more wind noise - i just adjust the squelch to compensate.
I find mine moves from time to time as you take helmet on/off, but still on the original one, and that was fitted a year ago
doesnt seem to loose it shape, maybe you are chewing it to much
give up / leave it alone and cope with it as is. 
