2021 - for those who, like me, landed here after the dreaded "button 15" failure I wanted to greatly thank the posters to this point, as it helped me a lot to get to resolution. And this is my first post here, I waited patiently for 24 hours to have the privilege but wanted to really share my experience and help anyone else like you have helped me.
TL;DR - managed to resolve issue by following above disassembly instructions and soldering in a 6mmx6mm tactile button in it's place, bought a 100 of them off Amazon for £6. If you DM me I can post you some if you are in the UK I am tempted to tear down the entire system and replace ALL of these types of buttons, as the new tactile one is 1000% better IMHO. A nice little affirmative "click" to proceedings.
Full (and long read, but I am excited by the results! So please bare with me):
My set is out of warranty, Thrustmaster was responsive to my lot, asking for proof of purchase and photo of original serial number sticker (so don't ever chuck them away..), but also a video of the fault. By this time, I had fixed it already... so not sure what the next steps would be.
Didn't fancy paying through the nose for replacement button, via Thrustmaster or some of the other recommendations here. Don't need a "mil spec" button, and the best price I could get from Mouser or the like was around £30 (that's more than 10% of the cost of a WHOLE NEW SET of HOTAS ). Plus, it didn't quite match the casing for the existing button, so... not for me.
I opened the casing, removed the wires from number 15, pushed in the 2 clips holding the button in the throttle hosing and using the advice above, wedged a small screwdriver in and around the plastic to disassemble the entire button.
As expected, the el-cheapo "dome" switch TM put in this very expensive case was metal fatigued. I used a needle under the plastic covering the button to pop it back out, but once pressed down, it stays down.
Could not locate a suitable 9mmx9mm replacement, so opted for something smaller but just as flat, as to not raise the profile. The little switches I got look like below and got them from Amazon (link here) and if you like, I can send you some :
Looking like this soldered in... be SURE TO THREAD THE WIRES through the hosing 1st! added a bit of glue underneath it to hold it centre in the housing too, and some hot glue on the solder to ensure they don't break (can also see the plastic housing chewed up by repeated attempts to open this button, more on this later... )
The next tricky bit was... assembly. My 1st attempt, when re-assembling, I pushed too hard on the red button, destroying the switch and shorting it. TIP HERE IS: the button housing has a small indent, so it goes in a very specific way into the throttle. Don't force it, apply pressure around the red bit of the button, not ON it, else this can happen:
The next issue was, the switch is made out of metal, so the spring would short out the switch. I was about to cover it with more hot glue, a perilous endeavour, when my genius girlfriend suggested using the actual packing material instead ! (This was an excellent solution, did not make the button spongy at all and good for the environment all in one. I used the duff 9mm dome switch as a template for size, cut a square and inserted over the button, like so:
While the button is still out of the case, snap the assembly back together (don't exert force on the red button if you can help it. TEST IT! Make sure it all still works before you make the effort of final assembly (did I mention I had to take this thing apart a bunch of times? yea...)
Lastly, make sure you position the indent on the case with the little ridge on the button, as it will only slide in one way (that's what she said...). Indent and ridge:
And that's it! Job's a good'n, and guys, honestly - the new setup really does feel so much better. Wish TM didn't cheap out on these s**ty metal dome switches. I will over time be switching the other 5 over also. And if you have some solder, and iron and the will to do this, it's real simple like. Take your time, read the advice and good flying, Captain.