I can't remember exactly, but a while ago my Statesman had the spoiler removed for a repair (big f-ing hail stone) and after the panel shop reinstalled it, the trunk leaked. They didn't seal it properly. A real amateur mistake if you had have seen it..
So, rather than root around and arrange to leave the car with them for another day or two so they could fix their f-up, I just did it myself.
From memory..
If you remove the inner trim, you should see keps nuts on studs. There's probably about 1/2 dozen. The studs mount into the spoiler and the nuts fasten the spoiler to the lid. You need to apply a small bead of sealant around each stud on the outer surface.
I guess you could use just Sika polyurethane to bond the lid in place, but it would need plenty of time to cure before you drove it. And personally, I know that stuff is really strong **** (I know because I caulk concrete pre-cast panels with it all day), but I still wouldn't feel comfortable relying on just the poly..
Have you ever peel a sticker of a painted surface and taken the paint off with it?
So, the Sika is only as strong as the paint's adhesion to the panel. I wouldn't.
Seriously, if you get a wax/chinagraph pencil from an art shop and mark it out properly and drill your holes one at a time and check and recheck each one before drilling the next, you'll be fine.
Otherwise a panel shop could do it for you. Shop around, the job is easy and should only take a couple of hours for a professional taking his time.
