I have that with my 08 as well, I was using 5w-30 full synthetic, and every other time i checked i was filling it up 1/4 to 1/3 of a bottle. I switched to 10w-30 and it seems to be just fine, dropped a can of sea foam in it as well.

It may be just because your running a thinner oil, if you are, or something completely different, hope my input helps.