I found this thread while searching for answers regarding a brown colored water leak that runs down the inside rear of my 172 ceiling-wall just above the window. I had previously bought ProFlex sealant after having two different RV shops recommend it. I removed all the existing old sealant and examined the spoiler up close. As everyone has stated, the spoiler is not a good fit. It bows out between sheet metal screws apparently due to differential expansion coefficients. Also, some of the screws are severely rusting out.
The leak inside the camper was a rust color so I surmised that the leak was from water passing over the screws and out through the screw holes. The screws I took out were severely rusted to the point that they were no longer #10 screws.
So, as others have said, all those screws should be replaced with Stainless steel screws. My temporarily fix was to re-seal the spoiler and to also put sealant over the screw heads to prevent further water infiltration. When the season is over, hopefully I can find an indoor space to fix it more permenately.