if it's the sender behind the dizzy........thats the water temp sender,u'll get no oil from there,if it is wet there then it's prob the rocker gasket.
the oil sender is just above the starter,if it's leaking there,pull the wire off,undo it with a 24mm socket (think thats the right size) thow it across the yard and fit a new one (about a £5.00-10.00). do not try to screw it all the way in,just till it feels tight.a bit of ptfe tape is not a bad thing but not really needed.