I have just changed the air filter and upon re installing the filter I noticed that there was not any type seal in the housing or cover groove yet, one upper and one lower is shown on the parts break down on the Honda parts direct website. Did Honda omit these on the 2000 California model? I purchased this bike new and with 23000 miles on it this is the first time that the air filter has been changed. There is apparently should be a gasket under the Charcoal filter as well. Also, I see comments on A sub filter. How often should this be replaced?