I’m new to the site, but I joined to get some advice and guidance. I’m restoring a 70 Challenger RT. I’m currently rebuilding the non-ac heater box. I ordered the Big non ac heater box seal gasket kit from Detroit Muscle Technologies. It came today and it looks like it has everything I need for the heater box. My problem and the reason for the Post is my driver’s side fresh air box. The rubber seal that seals out the air when the valve is closed is crumbling away. I guess I should expect that on a 50 year old vehicle. I’ve looked on several restoration parts sites and I can’t seem to find anything. Any advice or suggestions would be greatly appreciated.