rusting doors on driver's side along base. Was told it was a defect in the door. Car is 2008 Subaru Legacy limited with only 55k miles and in perfect shape. What to do? Ever heard of this before. Two garages had not but too expensive to replace doors for my budget.

The car originated in NH, moved to quebec and i bought it in Toronto. I garage it and hardly drive in winter. They still use salt although beet juice getting more popular. Thanks!

Perforated yet? If not, first try arresting the rusting process yourself. With a sturdy paint scraper and maybe a large screwdriver and small hammer scrape and chisel out the body filler putty strip along the bottom. Try to get it fairly clean, but don't go crazy. Then apply three coats of a phosphoric acid primer (Rust Reformer, Duro Extend...all the same recipe). Then ignore for a day and apply another coat of the now- black primer. Then ignore it until you toss this aging chariot. I would also remove any rear rubber wheel arch edge liner strips as they trap moisture and allow rust to start. I've found that lower mileage offers nearly NO immunity from age- related body rot. You've only a few more winters with this Subie body, so don't empty your wallet.

Thanks to all who offered great practical advice.