How do I clean this off the rear quarter window trim without damaging the trim? Also, what is it?!

 

The reflection was throwing me off for a minute.

It's not mold or grime. It's the rubber deteriorating caused by the sun.

Try mothers back to black to make it less noticeable and maybe reduce the damage a bit.

http://www.mothers.com/02_products/06108.html

 

The picture may not show it, but it's actually a substance ON the trim, it's raised and will scrape off a little.

I'll get some better pics up.

 

I have that too on my side window trim and mother back to black sucks after two days it will looks the same already tried i think the only option left is replacing the trim.

 

Have you tried using a little mildew remover on a small test area...maybe with a q-tip?

 

I use a toothbrush and car wash soap to get it throughly cleaned. you will see black grime come off when you do this.

I apply gummi pfledge to slow down the deterioration of rubbers. The only true fix is to replace. This will definately help but won't cure it. Mine still has spots but doesn't get fungusy looking anymore.