I know that this post is kinda old but I thought I'd share my insights. I have a 94 SSE too, and about two weeks ago I went to make sure my spare had enough air in it, and discovered about two inches of stanky a** water
in the groove that the spare sits in. So I soaked up the water and dried the carpet and put everything back in the trunk. To make a long story short I discovered it was the damn automatic car wash. Teach me for being lazy eh? Until reading this forum i didn't know how to fix it. I'll have to try that trick with opening the trunk and pouring water down the back window. I'll get back to ya!