This section was very kindly written by Michael Whyte-Venables.
You need to do this to replace the oil seal behind it (MIM 32x52x10) or to easily get to the neutral switch.
First slacken the dynamo belt and remove the pulley, allowing the belt to dangle.
It is best to obtain the special tool (25 90 81 00) available from Agostini's. Undo the threaded ring in the middle of the flywheel (left hand thread) one quarter of a revolution only. Then undo the 29mm nut (right hand thread) until it bears against the ring. Then with the aid of a soft mallet or a large piece of wood strike the end of the tommy bar (placed through the special tool) until it shocks loose. Removal of the fly wheel allows you to remove the inner flywheel case which will make access to the seal easier.
The bad news is that it may be necessary to split the cases to remove the oil seal (readily available from bearing stockists). One approach however might be to drill two or three 1,5mm holes through the steel body of the seal and then screw in short self -tapping screws against the heads of which some leverage may be obtained, carefully to pry out the seal. The replacement can then, having been obtained, be smeared around the lip with motor oil and driven back with a 200mm length of suitable diameter aluminium tube. In this way unwelcome schism may be avoided!