[cle73satellite]

the seals on the hatchbacks go bad. a decent quick test for that is to get some type of simple brush on paint and brush it on one side of the weatherstrip and close the lid. open it again and see where the paint has transferred. if there is a gap, there is your leak. if not, its probably not the weatherstrip.
ps, use a paint that u can get back off, dont want a colored weatherstrip.
with the spoiler, im not sure of a silicone or anything for it. is it just a bold that goes through it? cuz if so, the holes are all that could really leak. if its that some rubber washers would likely stop that.

hopefully this helps

 

[pSun]

Cle73satellite;

-I like the rubber washer idea.
-instead of paint on the gasket, I may try, colored water, but definitely something I can was off...I like the transfer marking idea.
-while I was reading your post I started thinling of the putty that is used around air conditioners; they was some very tacky grey putty like stuff in there when I took it apart.