I need help. 1965 300 4dr HT exhaust getting into the interior. The only thing that seems to help is running fan with windows shut and floor vents shut. Any other combination and after a short drive my clothes smell like exhaust. Thought it might be blowby escaping from valve cover breather, rerouted that into air cleaner intake but to no avail. No audible exhaust leaks before the muffler. It's possible that there are some in the muffler and tailpipe that I have not discovered. Car was quite rusty, is it possible that it is coming from the end of the tailpipe back into the trunk? Don't want to spring for a new exhaust if it is not going to fix the problem. Thanks.