well pressure in the cylinder, and heat from the warm oil will make the oil seals work a bit better.....when the engine cools, and the seals loosen up it can allow oil to seep past the seal and down the guide......common occurance.......pull a head off, remove a spring and with the valve just slightly off its seat wiggle it back and forth....a very small minute amount of play is acceptable, but I think you may find a lot of play in yours.....