I was wondering if anyone had come up with new seals for inside the flapper boxes. Just trying to make it so I get heat when I want it, and no heat when I dont. At the moment, it seems to leak a little, and can get a bit warm in the car. After looking at the flappers, it looks like they had some type of seal on them at one point, but not much left after 35 years. And, I have already heard the usual comments of "Buy headers and a jacket"

Sounds more like you need an adjustment to the valves. Like the cable needs to be adjusted.

So far as I know, ther're no replaceable seals for the valves. Internally, they seem to be indestructible, though the outsides can get really ugly.

I'd tryadjusting the cables. Sounds like that's all you need.

If the inside part has not become un-rivited, can it leak hot air to the front ? i don't have seals per-se, and do not get any extra hot air when off.

I tried adjusting the cables, but it didnt seem to help much. I think the housings are a little tweaked, and the spring tension is not enough to keep it fully closed. The original seal looked like it helped with this a little. I decided to buy some helper springs, to see if it will close a little better.

Helper springs is a great idea. I've asked this same question- think it was in August. In my flappers, the asbestos (I'm guessing) ring had come lose, so right now I have bad sealing too. I've adjusted and readjusted the cables too. In fact, it leaked just as much hot air with the cables disconnected. There has to be some kind of high temp capable stuff we can use to make new ones. Where are the fabricators? Hey out there! Bruce, or Engman, or Dr Evil, or ...

I was even thinking maybe a ring of high temp silicone would make a good sealing surface. I will try the helper springs first and see what they do.

It takes a LOT of prolonged bad weather to screw these simple valves up. And, they are very simple.

If you can make suitable adjustments via the cables, it's time to replace. These are probably the last of the914 bargains out there. Not only can you pick them up regularly on eBay for $20, but you can but brand new ones for $65.

Need heat - fix it!

BTW, I think you're correct about the asbestos ring. Doen't bother me though. I stockpiled asbestos brake pads 20 years ago & will never have to worry about idiotic dusting or premature wear. It wasn't broke, so I didn't fix it!