Costa's made quite a few changes over the past 12 months to address the rubber separation issues, including different compounds for both the hard and soft rubber frame components and how they are joined.
They know it's been a problem, and have worked hard to make changes to alleviate the issues. The newer, '17 frames, have noticeably harder rubber frame pieces. If you look at some of the popular frames, Corbina as an example, you'll also notice less rubber overall.
Some of the things mentioned above are on point. Leaving them on the mirror on a hot car, bug spray and suntan lotion, heavy sweat, etc. can all lead to premature degradation. PH values of sweat and skin oil vary from person to person. Some folks glasses degrade early and often, some never do.
The best advice I can give is this. Take em in the shower from time to time. More in the summer, less in the winter. When you shampoo your hair, use a bit on your glasses. Shampoo is gentle, but cuts the sweat and skin oils the buildup on your shades. It also gets the gunk out of the edges that you push into the frame when you rub them to clean the lenses. That gunk can cause clouding at the edges of the lens.
With all that said, send your problems back for repair. Costa is chunking any frames out that have the old compounds and replacing with new glasses with the new components. I've talked to some people who have gotten their old lenses in new frames. But by and large, many more are getting entirely new replacement glasses.
My problem is getting a good band that holds them on my neck when I pull them off or hang them on my cap. Think the last rubber that I put on the frames were Maui or something like that. It has lasted about a year and now the lubber ends are starting to slip. Wish they had a neck strap that was made into the plastic frame ear pieces so I could dangle them around my neck.
Check out the new Bowline retainers. 1 piece silicone tube. Fits tight on all frames. Heat and cold resistant, adjusts and stretches to keep them tight to your head when needed.
Costa Bowline 
