it coud be that the it's dirty but if it's the left stick than it's may be dying it's normal for the psvita 1000.

is the motherboard model the same as the old one? if not it's because the disc drive needs to be the same type of drive model to the motherboard model of the console that it came with so you need to get a disc dive model that is same type of drive model to your new motherboard model.