So, I think I'm at about 15,000 clicks on my XT. It's working fine, I'm just curious about some things. 1) What causes a shutter to go bad? 2) If excessive dust gets in to the camera, does the shutter wear out quicker? 3) What's the expected life on my shutter? I have seen a few numbers posted 4) Once a shutter dies, what's it cost to get it fixed? 5) Once a shutter is fixed, does it have another X0,000 clicks like new?