I've always ran valvoline 5w30 oil with a k&n oil filter since 58k and now I'm getting close to 100k. My question is my uncle game me two 5qt jugs of valvoline 5w30 high mileage synthetic blend oil and I'm afraid to use it for fear of leaks or any other issues if I decide to go back to normal valvoline 5w30. If I can't use it so be it its not a big deal but I figured I have it so if I can use it I will.