So I recently bought my FD, & it looks like water is leaking into the trunk (into the plastic trim on the inside of the hatch) through the spoiler mounting points. The paint on the spoiler doesn't match the car, so I assume it was repainted/replaced... either way it was removed at one point. Is there anything stock on the mounting holes that keep water from entering the holes... or should I just take some water-proof compound & put it in the holes? It's a real pain... for about 1 day after a rain storm... if I open the hatch, water pours into the trunk!

 

I pulled mine a couple of week ago and found a fair amount of rust around the mounting point on one side. I would assume you'll have the same problem. That would have to be cleaned up or replaced.

As for what the dealership use I have know idea but a light coating of black silicone would solve the problem. Just around the holes, also a good priming of the area would help prevent rust. I also learned that the spoiler was originally destine for a red car.

 

IIRC, there was a thin gasket of sorts shaped like the mounting surface. But I would think a little silicone caulk should work just fine.