If I remember correctly, the hype with Derlin was that it could be cast (injected) with extremely good tolerances, and provide less wear, noise and friction as metal. So far, so good, but the manufacturers did sloppy work on the parts the valve guides fitted into, on the casing and the valve itself. Result: lots of play. The nice thing about metal guides is they can be milled to fit what they fit into. Of course it doesnâ€™t matter if your valve guides are plastic or metal if you keep getting chocolate on them, Alex!