A couple cats put together some very nice, step by step, with pictures on how to remove back seat in order to get to subwoofer. I thought my sub was blown forsure, until I hopped on here and did some research. Turns out you can fix the sub simply by using a glue gun around the perimeter of the speaker/cone. I just fixed my sub on my 2001 Lexus GS 300, and now it works just fine. Big ups to the cats who put these intructions together, y'all are lifesavers!!!! Just want to spread the good will.
This one shows how to remove back seat:
http://us.lexusownersclub.com/forums/index.php?showtopic=46410
This one shows how to remove back panel to get to subwoofer (you have to remove back seat first):
http://bananags.grantham-international.com/GS_DIY/rear_deck/
Once you get to the sub, use a glue gun, and hit all around the perimeter of the speaker/cone. This will fix the problem, as the cone around the speaker rips really easy, and the glue will create an air tight seal. Good luck! Took me about 1 1/2 hours to take back seat out and fix sub, and only 20-30min to put everything back together.