This confirmed what I had been suspecting for awhile now. My Crossie was not at all well maintained by previous owners.

I ordered up a collection of repair and maintenance parts last week from FCP Euro based on what I was seeing in the forums here.

Went to replace the cabin air filter today and when I popped off the slider cover a small tree worth of leaves fell out onto the floor. So much debris was wedged in the plenum the filter took some effort to pull out. That's when I checked the codes on the filter...sure enough...it was factory OEM from 2003. Ewww!!!

I then focused on the task of clearing the debris. Used a zip-it drain clearing tool to dislodge the material then a set of Shop-Vac attachments for clearing dryer vents pulled it all out.

Popped in a new Mann filter and was done.

Surprisingly, the air flow didn't exhibit any issues before all this.