NG
The only way to really do a thorough job is to take the thing apart. With the switch rod removed from the shaft, below the total switch knob are 4 tabs that must be carefully straightened to remove the chrome ring that secures the horn button. After removing the ring, the button will come out (there is a spring underneath).
Then you can refurbish as necessary.
Again, be VERY careful when straightening the tabs, cuz they gotta go back
Merry Christmas
Jim