I've been putting off doing this as not looking forward to faffing around removing and refitting the diffuser - so many clips and it looks really awkward.

 

I wonder - could you just detach the side of the diffuser, enough to flex it down to drill the holes and attach the fin?

 

Doubtful. The cavity you need to access is covered by a plastic piece that would be in the way. At least one guy drilled large holes on the inboard side of the diffuser that he then put the screws through (without taking the diffuser off) but I don't recommend that. Kind of butchery if you ask me.

 

Honestly its very easy to remove, you remove the center diffuser 6x bolts, then you remove 5 more bolts. Then you need to pull on valence and it comes off. The sound when pulling is scary but nothing breaks. Just be careful where you sit valence on its scratches super easy

 

Excellent advice that nobody has mentioned before. It scratches if you look at it wrong. Have a nice soft blanket to put it on as you work on it.

 

This what I did. I used tape on the diffuser to mark where the holes go and drilled the holes from the outside. Then I pried apart the inside two pieces of the diffuser and inserted the screws to attach the fins. Worked perfectly without disassembling the whole diffuser.

 

Which screws is everyone using ? Didn’t purchase the expensive OEM ones.

 

I'm going to give it a try as removing the entire diffuser is going to be a faff. I'll document the process with pics when I get around to it.

See pics below (note diffuser is already removed):

• Red dots showing the drill holes required on the outer diffuser trim (not accurate distancing, just for illustration)
• Yellow dots shows the screw attaching the two diffuser pieces that need separating when attaching the fins

Pics lifted from this video:
EDIT:

Definitely doable without removing the entire diffuser:

 

I posted this a while back. #12 Stainless steel Sheet metal screw in ¾ inch length.

 

I learned this the hard way

 

You and me both. ☹️

 

I ordered a new piece

 

Lol. I have no doubt. I'm close.

 

Do you have the part numbers for the 4 piece underbody aero as in the pictures.

 

9GT 807 913 A