Thats a leaky o ring and takes minutes to fix and cost pennys.

If you have oil in the cap then its the internal and more difficult o ring to replace but that looks more like the outer one.

Simply take the cap of and mark when the dizzy is with tipex on the dizzy and head, take a note of which way the arm is pointing as it makes it easy to re-insert.

Undo the 2 bolts holding the dizzy on and pull it out to reveal the o ring.

Replace this and re-insert the dizzy.

If you marked it well you shouldnt need a timing gun to retime the engine.
