When I had my 7.3, I experienced the dreaded connector boot blow off a couple of times. I blamed it on the oil from the CCV vent tube getting into the intake, getting the tubes all slimey and causing the connector boots to loose their grip on the tube.
After the 2nd time, I removed the connector boots from the tubes and cleaned them up real good with some degreaser/engine cleaner. Then using a pliers, I CAREFULLY bent the end of the tube outward, in effect putting a very slight flair on the end of the tube. That helped to keep the boot and clamp from coming off the tube. Oh did I mention, I double clamped the boots too?
Then I did the CCV mod previously mention above. So by doing the cleaning I did the fix. By doing the CCV mod and flairing the tube, I added a dose of prevention to keep it from occuring again.