wel this guy asked but hasn't been back---but on a flathead, there are two kinds of valve guides--early ones are split so they can fit around the valve stem because the valve tip is huge like a mushroon---the later ones are one piece but both kinds besides maybe letting oil up the valve stem can leak pass a defective rubber seal that fits arond the guide where it fits in the block--these old seals and new modern oils don't mix well and the intakes could be sucking up considerable oil and the valve will deflect it over toward the sparkplug area where it could get arond/thru the threads(partially stripped after 70 years) and leak out pass the 18mm copper gasket--------