If you still have old Blackberry Curve 8520 or 8530, generally you will get the problem around the buttons, volume button, shortcut button, at left and right side of your Blackberry, the rubber or plastic of the buttons are damaged because of life time of usage.
|Damaged button of Blackberry 8520/8530|
In the smartphone/phone component store, or online store like Aliexpress.com you can get the chassis. or you can search on the Internet using key word : chassis for Blackberry 8520/8530, you will get many results.The price is not expensive, below $10 US. including the components like earpiece, buzzer, buttons,etc.
After you get the chassis, you can reassemble your Blackberry 8520/8530 using the new chassis.
How to Deassemble and reassemble, you can see on Youtube, there are many video you can see there,
one is :