Swapped out my spark plugs a while ago which temporarily fixed a misfire problem. Then a few weeks later I started getting the misfire again. I remember when I was taking out the old spark plugs, one of them was broken completely in half. I didn't think anything of it but now I'm thinking one of the pistons is coming up too high and hitting the bottom of it, which is what caused it break and most likely why it's misfiring again. So. Pricey or reasonable?