I thought I should share this:
The joystick of my W800i gave up on me very soon because of dust inside of it.
I disassembled my phone and tried to blow it out with an air compressor. That did the job for around a day or two.
So I bought a replacement joystick on eBay for little money. But the solder points are way to small for me, so I didn't use it.
Next thing I tried was injecting some pure alcohol in the joystick with a small needle. That did the job for several weeks.
I should warn you that you can damage your screen by doing this. If you spill alcohol on the back of the screen, the reflector film will come loose.
The last solution I used was injecting some WD40 (oil-spray) with a needle.
This works very well. I did it more than 6 months ago and the joystick still works perfect.
Good luck with it.