Rear quarter window discoloration

I've posted this on another forum and I am posting it here to see if any other owners on this forum have noticed the same thing on their quarter windows.
I've noticed a discoloration (not condensation) at the bottom edges of my rear quarter windows. It is more pronounced on the right rear quarterglass. I know that on occasion I will clean the area underneath that edge(that's where the rainwater pools)...but it's beginning to look pretty bad. Anyone else notice this on their quarter windows?

I've attached a pic of it (look at the very bottom of the edge.. the lightish gray area)...

Well, I did use some of Eagle One's Wipe and shine a few times in the past with a soft cloth to get some of the crud that accumulates in that area (under the bottom of the glass)...that could be it. However, I checked a few of the dealer lots in my area and some the older '05/'06 Stangs are showing signs of the same thing. It must be the rainwater that pools in that area and over time it slowly dissolves the black tint area behind the glass...that's all I can think of. Really weird.

I'm thinking of covering the quarter windows with some louvers...it's a shame because I love the look of the rear quarter windows...this problem is definitely more prevalent on the 05 and 06 Stangs...07 Stangs will be next...it's just a matter of time I guess. If anyone comes up with the solution (without having to rip out and replace the quarter windows), please let me know.

Jared, I believe I've found a temporary solution. ...I took a small piece of cloth (baby diaper) and lightly soaked it with 3-in-1 oil and folded it so that it would be shoved up behind the bottom portion of the glass. With a back and forth motion I was able to make the "discoloration" disappear. I then used a dry piece of the cloth to remove any excess oil and cleaned up the rest of the window with my glass cleaner. It's a 100% improvement. Of course, the real test will be to see how long it will stay this way and I'm sure future rain will most likely bring the discoloration back...this might end up being something I will have to do monthly or so. Or maybe silicone grease or silicone spray might work as well and last longer.
Give it a shot.
I couldn't get some of the discolored area on the vertical edge since it's almost impossible to get the cloth in between the glass and the surrounding body frame.
BTW, it's been three days (with some rain last night) and still looking pretty good.