Lunati Valve Stem Oil Seals are available in four options, each with their own advantages. O-ring oil seals use a standard retainer and oil splash shield and do not require machining. Umbrella seals are used with larger than stock springs and also do not require machining. Positive-stop Teflon seals are used for double springs and require head disassembly and some machining on top of guide. Small diameter Viton seals are used for triple spring applications and require no machining