|i once had to use my mark2n with the 70-200 to break a face-first fall off some boulders. landed hard enough to eject the battery. i put the battery back in and fired some test shots and realized something in the lens was loose. canon needed about $125 to make it right. the body was fine.
about a year later, i was shooting a story about a swim team and stepped up to the pool deck to get some wide shots of the kids diving in. there was no non-skid surface and when i stepped too close to the edge, me, my mark2 and the 16-35 attached to it went flying, into the pool. i hit the bottom and was fully submerged for about 5 seconds before being able to get out of the pool. popped out the battery and card and dried everything off. an hour later, i was shooting another job with the same gear (except for a different flash card). the mark2 went on to shoot another 100,000 frames before the shutter wore out (it made it to well over 400,000 frames before dying). it took almost $250 for canon to refurb the body. the lens is still cranking (and has no mold or fungus issues, either). my cell phone, though, was toasted. it just never came back. my remote car key died, but started working again after a few months. weird, that.
after nearly three years of constant use, my 70-200 started acting up (like not working, showing aperture 00). upon inspection, i noticed the brass receptors had divots from wear. it worked fine with my 1.4TC attached, so that was how i used it...until i dropped it a couple feet and knocked something else loose. this time, canon only needed $65 to refurbish it.
given the amount of use my equipment gets, all this was somewhat expected. i wish that could have been said for what happened to my 24-70. i was simply walking across a parking lot, looking at a sign i wanted to shoot, when i stepped over some broken pavement and twisted the ever-lovin crap out of my ankle. i was going down face first and lost my grip on my mark2. it slammed into the parking lot so hard that the 24-70 ripped itself off the body. the mounting ring was still attached, with all four screws sticking out. the lens went rolling, stopping out in the middle of the road. that was not pretty. all the same, for a measly $110, canon put humpty-dumpty back together again.
bottom line, things are going to happen. when they do, your best bet is to get them checked out at the factory, especially if it's good glass. the main thing, though, is when you write up your work order, make sure you request a complete evaluation and cleaning. if you only request a specific repair, that might be all you get.