Dingoonity.org

 First off, welcome to the community! Also welcome to the club of the sticky buttons. Unfortunately, it plagues a lot of us, however there are a few many options to tackle. The new 3-D printed buttons and D pad are your best bet as far as not having to modify the front-face/casing with larger holes.
 People use all kinds of things for the D pad modification, the original Dpad from a GameBoy, some people glue a ball bearing to the bottom of it for smoother diagonals, etc. 
 But as you stated earlier, all of that comes with the price of a major crafting experience. For what it's worth, it's already difficult enough just to open up the GCW0 and replace the buttons with ones that fit the holes. So if you're afraid of doing any more work than that, I would stick with the 3-D printed options. Otherwise here's a thread with lots of modifications as well as people asking questions about modifications that you could study and get some more answers from:
http://boards.dingoonity.org/gcw-general/(gcw-zero)-mod-custom-10297/

 The membrane replacement under the D pads and buttons is solely up to you. To replace it would seemingly be unnecessary unless to fit your comfort level of hardness pressing. As of right now it seems that @ithic.com does not have anymore  of these membrane underlayments for sale on their site, but supposedly they are a bit harder to the touch, making your D pad and buttons a little bit more stiff as opposed to loose. Which to be honest, I would prefer myself.

 And to answer your question specifically: the Wii U buttons and Dpads would require you to create larger holes in order to fit them. I have ordered those buttons and Dpad to compare, and they are definitely larger and require (as you put it), a "large crafting experience"

 Hope this helps

However, in the meantime, I've achieved very great and durable results on the buttons without disassembling the console  By using a fine strip of cloth that I soaked (Slightly) in WD40 , holding it firmly between thumbs and forefingers then rubbed back and forth forcing on the edge of the buttons. Then, clean off the excess with a dry cloth and wait a bit.
Also good for the dpad (WD40 cleans well but is not very durable as a lubricant), depending of the Zero.
EDIT : You can do this with rubbing alcohol too.

Why would you use WD40 instead of alcohol to clean it? WD40 leaves a nasty fragrance, it also attacks certain types of plastics and paint and definitely rubber (our membranes are probably made of silicone so that's not the major concern). It creeps into surfaces which is the last thing you'd want underneath dpad/button membrane. It doesn't have lasting lubrication.

It's great for cleaning grease off a car part or loosening up a dirty bolt. Just use rubbing alcohol to clean the DPAD/buttons and apply a small amount of silicone grease with a toothpick. Any car parts store has little packets of them up by the cash register, called 'spark plug boot grease' or 'dielectric grease' for around $1, good for 1000+ applications to a GCW.

Hi! Thanks for your answers. I will go with the 3D printed buttons. Has anyone ordered them from europe? How long was the shipping time ?

@Swarmadd, you could update the wiki with alternative suggestions.

And another quick question: How can I identify the right 3d buttons and d-pad? They all have another button and d-pad connected by a thin piece of plastic. I know it has something to do with the printing process and the orientation but for me they look all the same...

I haven't fully understood your second post, but I've read this : http://www.gcw-zero.com/news.php?id=16 and I think you must choose the smoothest side of the piece for the sides, so it won't jam/clog. That all I can do ^^ Just wait for someone who already had these buttons in hands..

 

Thanks :-) Yeah the buttons look nearly the same but it's the smoothness which makes the difference.

So with the help of the two tutorials here in the forum (big thanks to fosamax and cheesecake) I was able to replace the D-Pad and the Face Buttons. Unfortunately I damaged the slim cables of the L and R Button while opening the GCW Zero:



So the only way to fix it, is to solder it, right? I don't have any soldering experience but I will get some help from a friend this weekend.

For now I would like to test the new buttons but without the L and R buttons I cannot navigate to the "emulators" tab. is there any other way to get there without L and R?