I have a STF-8300 that is 2 years old. After one year of use the sensor window began to frost. I baked the desiccant plug and everything was fine until recently. The frost has reappeared. I baked the plug per the instructions but that did not prevent the frost. I then baked the plug, reinserting it into the camera for 24 hours, and then baked it again. I did this three times. It did not correct the problem. Now, as soon as I turn on the cooling the frost appears and makes the camera useless. This happens even when I run the temperature regulation at 3-5%. I have checked the O-ring and it is fine. How do I correct this problem?