I belive there was a service bulletin a long time ago for the rubber tear drop shaped boot that goes around the sterring wheel shaft through the firewall that was prone to "leaking". Had this issue with both of my old CSVT's. THey would crack and aloow heat to leak through, epsecially where it's located, you get the lajority of the heat from the rear cat. Felt like a hairdryer was on contantly blowing at my ankles. I believe you can do it yourself, have to disconet the the "CV Joint" by the interior side of the firewall to slide the new boot over.
Edit:
It's #2.. about 13.00. If that's not the case, check for rust. in the floor.
