Mine is a 2009 too, so maybe that's about the lifespan of those clips. I doubt if this has ever been kept under cover. It has a label that says it was bought in Wyoming so it might have been kept there for the first few years. In my dreams, Wyoming is not the summer oven that Texas is, so it may not be heat as much as just aging and oxidation.
Where did you get your replacements? I found some on Amazon, but it was for a package of 20 I think. At most I'll only need 4.