im not an expert but this what i would do
in order:

1 change face plate one of my buttons a wile back lost a rubbery part inside and i just changed the plate and it worked

2 look for hax my friends analog stick dident work and kept going up luckly there was a cool program that messed around with its sensitivity not shure if theres one for buttons thogh

3 rip somone off with it and use cash as a discount for a new one
i let sonny fix my old fat one and i got it back 45days later

4 if you have special love for it you can give it to a game trader store
were i live the fix them for about 40$ and they don't care about mods they know what's up :)

5 if u hate all these options then you can play it like it is untill money rolls your way

good luck i feel your pain ive been there