Oil leak from starting handle shaft

Hi All

My 1950 11BL has become a little incontinent from the front of the gearbox.  It appears to be coming from the oil-seal around the starter handle shaft.  While the additional rust protection this imparts to the underside of the car is welcome, my wife is getting a little vexed about the fresh oil puddles on the driveway whenever I return from a drive.  So, how easy (or otherwise) is it to replace this oil-seal?

thanks

Paul