corrosion from the previous water damage is the likely culprit. you can of course still clean it but ultimately you know you will have to replace the camera etc.
Here is my answer to a similar question. "Rice does not work. It will not prevent corrosion! The very first thing you want to do is to stop using your phone. Stop right now and do not continue to charge or sync it. The very next step I would do is to disassemble it by following this guide. Take a careful and close look at all components and connectors. Truly assess the damage. Look for major corrosion, evaluate the pins in the connectors etc,. Take a look at all connectors as well as cable ends. After that I would suggest that you clean it a couple of times in sterile water, not drinking water. Use a soft brush and clean it very, very thoroughly with the sterile water. Depending on the amount of corrosion, you may have to remove all the EMI shields. Once you got the gross contamination cleaned, use 90%+ isopropyl alcohol and clean your parts some more. For a proper cleaning, use this guide. It was written for a 3G but it is still pertinent to your phone as well. I can not stress the importance of a good cleaning enough, so do it over and over while replacing the alcohol after each cleaning. Do not use compressed air for the cleaning since that can drive liquid as well as corrosion particles into areas that will cause trouble later on. Do not use drinking water, if you need to use water, use sterile water. Also, you do not need to leave it to dry for a day. Isopropyl alcohol in the higher concentration will evaporate quickly and dissipate the water. The importance here is the cleaning. Do not forget to replace the battery. This is a must and not an option. It will fail if you do not take care of it now. Keep in mind that water damage is the hardest to troubleshoot and to repair.Hope this helps, good luck.