about psp covers problem

My PSP has bought a year, and today I found the question, is the psp covers left angular crack a small mouth (also two mm so long!) I don't know when the crack. I decided to change the psp covers, but had never asked about psp covers, also do not know the game shops have shell, also don't know how about quality, listen to my friend before seemed to say, he said can only in the back of the front of the bad match, and the price is high, in addition the upper right R key stretch not how well I don't know that this little buttons can change? The psp covers?