Does this happen often? Not really as i have a fleet of these trucks i service. Have ran across three lifts total of hundreds i have worked on. If you suspect a breakage or intake manifold leak, check plugs and if they have white powder look then you can tell which cylinders to look for. Of the 3 i have replaced, i have found them cracked between #1 and #2 and usually the flange will be involved. My opinion it isnt a problem due to fact of huge numbers of the k-series engines i have serviced since their introduction and just 3 in my opinion doesn't call for a concern.