So that explains why my dash was full of dust! Discovered when replacing heater core and motor

 See attached pics. Mysterious hole bust in heater distribution box!

I finally got around to taking out and replacing the heater core and blower (blower had failed, figured I'd replace the heater core anyway at the same time just because it was easy while I had it out (turns out old core is fine, so if anyone needs one please PM me).

When I got it all apart, it was obvious why the dash space was so dusty - a bl***y great hole in the curved inner surface of the central distriution channel.

I cannot for the life of me imagine how it happened. Its not a small hole and is accomopanied by a substantial crack running up that face too.

Anyone ever seen anything like this? Its not as though its even an easy area to get to and the plastic itself isn't even brittle.

The question is what to do.

I could just get it plastic welded I guess, but I think the area concerned has a moulding in it specifically to split the air flow. As ususal, I'd prefer to do things properly too.

A new replacemenbt box (I think they are only available as complete shells, even though this surface is a separate part riveted on) is part number A0008309603 I think, no idea on price or availability though.

The other alternative is has anyone got one from a G they are breaking?