I recently bought my 99 grand prix gtp and was planning to put sound system in the trunk when I removed the spare tire I noticed there was a lot of water accumulation. At first I thought it was melted snow that had fallen in when loading groceries. Wrong. My spoiler was letting in trickle amounts everytime it rained or snowed. I took the spoiler off and cleaned the area good. Then applied a weather proofing silicone sealant to the bolts and holes. Make sure you wait at least 5-10 minutes after applying before tightening. Hope this helps someone else