One of the most rust prone areas of most cars is the sill area. This is especially true with cars that are operated in area's that use salt for snow and ice abatement. I'm sure that salt gets trapped in this area and as a result you have a rust problem.
Funny I come across this thread, I just posted in another about rust. My 2010 has visible rust there. Driven daily year round in the "rust belt" salt states.... WI / IA I wasn't going to bother repairing it, the car has 236k miles and I am sure this will not be the death of it. Hope it keeps going! Planning on taking a few trips this year with it!
