Heater Box Question - am I missing seals?

[NC_John]

I tore apart my entire heater system inside and outside the cab. It was completely jacked up with leaves. In fact, a previous operator was trying so hard to open one of the levers that they broke it (so I have to rebuild the heater controls). The damper door they were trying to open/close was packed solid with stuff. I took the entire assembly apart, cleaned and serviced it so it should work like a champ.

Anyway... Please take a look at your heater boxes- is there a gasket or seal missing on my heater coils? Seems to me there should be something there to keep more air in the cab. I can't tell from the parts vendors I checked out if there is supposed to be something there and the service manual doesn't have enough detail...

Thanks!