The original-equipment type oil seal is under the valve spring retainer, a square-cut O ring that can't be seen without removing the keepeers and the retainer. There is also supposed to be a sheet metal cover over the top of the spring that deflects oil away from the top of the guide, along with the O ring keeping the oil fron running down the valve stem.
Umbrella-type seals, or "positive" stem seals that attach to the top of the guide are aftermarket parts, not original equipment. If you choose to install them, be sure and remove the original seals, as too much sealing can starve the guides for lubrication, and cause very rapid wear.
Jerry
