I just bought my first Duramax, 03 K2500. I went in and replaced injectors and under the upper valve cover there was indicator marks where two of the rockers were impacting the upper valve cover on each side. Valve cover height seems fixed as well as the rocker assembly. While there I adjusted valve last lash. Any ideas of the cause and repair? It has 300k miles with good oil pressure and zero blow by at idle. Outside of noise I can't think of any real harm but it is concerning.