back when I was college I used to do long (I always thought too long, prob many over 12k n 15k too, wasnt always keeping track) oci on a kia. I was very broke then and didn't really keep up on car maintenance honestly, always Quaker State Conventional or Pennzoil Conventional. but car had 215k+ when suspension rusted away from body beyond repair, never a engine or transmission problem, original transmission fluid, antifreeze I'm sorry its sad to say. I always thought was going to hurt it but the winter weather is what killed it.