I believe the part to replaced is called MB Contact Unit(755).
See part number 264 below (link: http://www.searspartsdirect.com/par...arts/Model-NEX3KS/0996/0500140/50037220/00006).
The original part number was A1773802A, but subsequently has been replaced with A1876371B, maybe because the original component was found to be defective (just a guess).
The price seems to be around US$20-30.
Hi thank you for your explanation. I brought the lens and my camera to Sony and have it fixed.
At first i thought the lens was the one which not working well, but it is the camera instead.
it took around 1 week+ and they replaced the #264 foc (since my camera left with 3 months warranty) and it's been working fine now.