tacho drive shaft - scrolled or not?

Whilst trying to stem the oil leaks on my motor, I noticed that my tacho drive shaft has an oil scroll cut into it, which seems to do a wonderful job of dumping oil onto the outside of the engine. This scroll seems to make it pointless fitting an oil seal to the housing, so I was wondering if this came from another version of t he Norton engine?

Scrolled is earlier I believe. Unscrolled later model. I obtained an unscrolled one then had the aluminum body bored out a bit to press in a rawhide seal and it has not leaked since.