Hi Rahesh,
Let me begin by saying that the following IS NOT endorsed by Microsoft and I cannot warrant any damage that may be caused to the controller through this process.
It sounds to me like battery corrosion which is a pretty common problem in any consumer electronic device that uses batteries.
Here's a good video which goes through the steps you will need to take to clean this:
https://www.youtube.com/watch?v=ITKmMipctsk
Best of luck. And remember that not enough is better than too much.
Chris
