I would buy a new fender and replace.what you should be worried about is why is it rusting ? was is scratched or dented before on the same spot ? did you buy car brand new ? If you got it brand new and you are sure of history no point replacing fender,

 

I bought it when it was 3yrs old out of Quebec.. so it was winter driven up until that point..

I assume that either dirt or water got trapped behind the fender liner and sat there over time and rusted the fender.. friend of mine in town has an 08 and he has rust in the same spot so I assume its just one of those spots that tends to rust on IS's..

I've had the car oil sprayed twice in 3 years since buying it

 

I would get it repaired. Why waste hundreds when a body shop can get that like new?

 

My only concern is that in not spending the extra hundreds I'd just be wasting the hundreds I spent to have it repaired. Although it is very minor.. just no telling how deep it goes but I guess that would be the job of the body shop.. to make sure that all the rust is out before they prime and paint.. I don't know what to do haha I'm going to Cedar point Ohio this weekend and my contact at Lexus is off next week so I have a few weeks at least to mull over the decision..