I suspected it was that- thanks for the confirmation. (Sigh) and another EBAY order coming up!
Cedarwoodron
That sounds a lot like a winterization hatch:
The real one is used to redirect warm radiator exhaust air back into the carbody, to keep it warm. It can be "turned on or off".
Ed
On some F9 models, I notice a raised square feature just after the standard roof fans-what is it and is there a detail part available these days?