I know I never did until after adjusting the valves many times, changing the timing chain, and I finally noticed this at the vary end of a complete engine rebuild. I wonder I Toyota is sending me the plastic ones or the metal ones? I read somewhere that Toyota makes a two piece one that clamps on and allows you to simply cut the old one out and put the new one in place without removing the head bolts, which would mean you should also pull the head to replace the head gasket. Does anybody know anything about these supposed two piece replacements?
