while driving yesterday at highway speed i happened to see that my air filter dummy light came on. when i stopped and looked under the hood to see what the guage said concerning my true filter life, i noticed that the reset button/plug end of my filter guage had cracked completely off and the guage was missing the internals. the only thing i found was the spring. currently have about 120k miles and changrd the filter maybe 30k miles ago. any ideas why the guage cracked open? any way to tell my true filter life? thanks for any thoughts.