I pulled off my front spoiler to replace it with the Aerokit version and was researching the finish on the center piece. I noticed that my car does not appear to have a piece that another members GTS has. In the picture below (arrow points at the part) there is a piece that looks like it covers the bottom part of the center radiator possibly held on by 4 plastic rivets.
Prior owner of my GTS had a Escort 9500ci installed and I am guessing that the installer forgot to put the part back. Can anyone verify what part# the piece is?

 

Not the best picture to be sure, but I believe that what you are pointing-to is what is defined as "air duct". Part # is 99150599300. PET lists quantity of "2" but show one in the following diagram.... Hope this helps.

 

Saw that on the diagram too, pretty sure those are plastic pieces that go into the smaller air openings since it lists 2. It seems what I am missing is cover for the center radiator.

 

Could be, but based on the shape of the part you point to in the picture, I would still suggest it is the air duct part... Diagram doesn't show this part as sub-*** to the air opening grills, but line leads to directly under cover. And just because there are Qty of 2 listed doesn't mean they are R/L-- could simply be two parts directly together. Wouldn't know for sure unless you took a better picture. And, Center Radiator cover doesn't look like that. And note that in the diagram, the parts shown are specific to SD cover and NOT the standard cover on base and S cars without SD. This part does not appear in the diagram for non-SD.

Good Luck!