Well, I'm not sure what the problem was with that first clamp, but I went on to the next one, and it crimped fine, so I went back to the first one, and was able to get it crimped. For some reason, the first one didn't need as much crimping to get snug, which made it an unfortunate one to use as my first (I've never had the "pleasure" of a CV boot replacement project before.

So, the left side is done, and I've smeared some grease in the right side's outer joint through the gaping hole of a tear in its boot so the car will be driveable (although we will keep any driving to an absolute minimum) while I wait for the new clamps to arrive, at which point - oh joy! - I get to do the right side. Thanks to everybody for all the helpful suggestions along the way.

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2003 X5 4.4i
1992 Porsche 968
2007 328i
2014 Subaru Forester XT