Is there a way to replace the power button?

Hello

I have a Macbook unibody white late 2009 (A1342)

When the macbook powers up, the apple logo appears with the loading bar, and then around 15-20% it shuts down.

I tried:

- another battery

- without battery

- other hard drives

- another logic board

...all of which, without success..

So i came to the conclusion the problem must be the topcase, and more in particular the power button. Any advices ?

Is there a way to replace only the power button with some tinckering?

Funny enough i have another of the same macbooks where the keyboard does not work properly (but the computer boots without problems)

Could I use some parts from it?

Sry for the long question!

P.S. I know it's old macs :)