What does shutter failure look like?

In January 2008 I purchased a used 30D from Adorama, hoping to take advantage of 2 generations of advances since my 10D was made. I opted to purchased a used "as-is" body rather than a refurbished unit, and have been paying for that decision for almost 7 months. More after the bump.

The first indication that I might have a lemon were the rampant "err99" messages I was getting during my Belize vacation. The progressed during the trip that they occured about every 5th frame. Very frustrating! So I went the body in for repair at the Canon Service Center in Irvine, CA. Their assessment and repair was:

We have examined the product according to your request, and, it was found that the adjustment of the shutter assembly was incorrect causing an error to be displayed. Electrical adjustments were carried out on the shutter assembly. Other electrical adjustments and inspection and cleaning were carried out.

Ok, that sounds... interesting. I am not exactly sure what an "Electrical adjustment" is. But the camera was returned to me and was err99-free! Yay. After a few weeks of shooting, I noticed something very disturbing:

What the heck is that? So I did some research into what could cause this arcing. It was not good. It was almost certainly impending shutter failure. So I did some testing to see what settings would reproduce it. Turns out it was most evident with high shutter speeds, usually 1/2000 or faster. Apparently, there's some sort of damage to one of the blades of the shutter which is letting in a bit more light along its path of movement. Here's an example of what it may look like (this is not my shutter):

Yikes. Unfortunately, I noticed this problem only 1 week before my Great American Road Trip. I did not have time to send my camera in for repair, so I would have to mitigate the problem until I got back. Fortunately, most of what I was shooting was static landscapes that did not require high shutter speeds. During my trip I noticed that when I was shooting a large blob had showed up on the sensor:

I suspect that was another chunk of shutter blade. Damn. Surprisingly, the camera made it the rest of the way through the trip without any major failures. Upon return I did some further investigation and found that the arcing was evident in the first back of pictures I took after I got my camera back from its "electrical adjustments".

So back the camera went for further repair, this time, they were gracious enough to cover this repair under the warranty from the previous repair. So we'll see how the camera does now. I just got it back but haven't had a chance to do any shooting.

The lesson here is be careful on your used purchases, even from a venerable reseller such as Adorama.