That is really wierd, I had this problem when I got my 94 GSR. I racked my brain trying to find the source of the leak, but to no avail. I finally just drilled a few drain holes under the spare and put it all back together, now the water doesn't collect and it doesn't stink up the car. I did that about 2 years ago, I'm sure it still leaks but I really don't notice it and actually forgot about it until I read this thread. If you don't mind drilling a few holes in your floor then this seems to be a good easy solution.