My 02' LS 430 UL had a filter under the front seats. The filter was the size of a cigarette box. I just blew the filters out with compressed air every so often and the air flow was excellent.
My 08' 460 has poor if any air flow. I am going to blow some compressed air into the seats to see if I can "back flush" the air canals.
Who knows.. It's worth a try.