I have a spot on my sensor. Don't know how it got there..probably changing lens..but I'm careful here. None-the-less, I have a spot..rather large on the sensor. I have tried the dust removal feature numerous times but it remains. It is most likely not dust but something that was wet and now dried onto it. Shows up on some pics. Anyone know a safe method in which to remove or should I take it to a dealer to have it cleaned? Thanks in advance for help!