Do you have the reciept for using the Valvoline fluid? Does that fluid claim to meet or exceed the OE requirements for you Kia? Warranty stuff is funky from state to state. Here in MA you do not have to go to the new car dealer for routine service but do (it's in some writing) have to use their parts.
An example was to replace spark plugs for a customer with a Hyundai something and if they weren't from the dealer it voided a 100k warranty! She got em as none near my shop and they were the identical NGK plugs I had but in a Hyundai box - no kidding.
Freqently the oil manufacturer will back you up. I'd be on Kia's hotline asap with as much info as you have and documentation available. Best I can say is good luck. You'd win here I think,
T
Tom Greenleaf - MetroWest Boston - USA
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http://www.autoacsystems.com/tomgreenleaf/