yes, there is a rubber Oring which can leak. Unplug 4 HT leads and king lead to the dizzy. Remove 2x 14mm bolts on the dizzy bracket and slide whole unit out. (probably easier to remove the airbox first..)
when removed, keep rough position of spindle to aid reassemble but don't worry too much, it cant go back in upside down as the keying interface to the cam shaft is slightly off centre anyway so can only go back on in one position.
you can see the rubber oring in the above photo on the non spinning part of the shaft/ spindle (NOTE: back cover of distributor is not shown)
Toyota main dealer will sell you one. (the rubber Oring that is..)