I have a 1975 450 sl with 150,000 miles on it and I am contemplating a valve job. The top half of the engine is brand new but I still have a very loud tick. It sounds like a disel engine it is so loud. I have no vacuum leaks and good compression (160 lbs +/- 10) across all eight cylinders. If I have a valve job done, will the increased compression make me start burning oil or worse yet, blow a ring? Also, I am concerned because you say that when the valve guides are so loose that the make a lot of noise like mine the head will have to be replaced. Is this always the case? Thanks for any feedback!