This would be a problem if the lens/body combo is supposed to be weather sealed! I was under the impression all the white "L" series lenses are water sealed. I don't know about the 5D.
They are weather sealed, not water sealed. Dust, sand, mist, rain etc.. are mostly blocked. They are certainly not weather/waterproof and care must still be taken. I have been in steady rain as well as off road dust storms without anything getting into my 1 series bodies.
Even with some wiggle I have not had any issues whatsoever with weather getting into the body and affecting the images. A bit of wiggle in the lens/body mount does not mean that it is not still weather sealed.