I have used a baking soda and water solution on my car to get rid of corrosion that was keeping the battery from connecting, and one full cup of a water-baking soda solution (very little baking soda, too - probably 1-2 TBSP, but I can't remember right now) will remove all of the corrosion very quickly.

Since you're using this on a keyboard, you should probably take more caution not to get the rest of the keyboard wet - perhaps dab the solution on a cloth or paper towel or q-tip or something and rub that where needed. Also make sure that the unit is thoroughly dry before starting it back up - a hair dryer will speed up the process dramatically.