Missing piece DW717XPS?

[Wlkes]

Hi all,

i have a type 3 dw717xps mitre saw. the other day  piece of wood shot up and, as much as i can make out, hit the dust port.

a solid black plastic piece then got caught up in the saw and was completely demolished. thing is, i can't make out where it came from, i can't see any broken off pieces. the only thing i can think it may be is a part that sits it the dust port (see photo) and would basically snap into place. Does anyone with the same model have this piece in theirs? On a type 3 parts list the dust port is no. 255 but i can't see it by the diagrams.

Any ideas what part fixes just inside the dust port??

Sorry photo not uploading and trying to fix with Admin.