Took our 13' Sonata 2.0 turbo in for an oil change. The dealer told us that if we don't use a Hyundai oil filter then our engine warranty would be void. They claim that aftermarket filters don't meet Hyundai's specs and will void the warranty. I explained that the filter I wanted them to use has a backflow prevention feature and says it meets all manufacturers specs. They responded that Hyundai won't accept any filter except their own. Any input on this?