The optical distributor that is mentioned gets oil on it when the shaft
seal fails.  When you replace it with a rebuilt one.  I bought mine from
Nissan since I did not want to screw around with aftermarket, and it
worked great.  Yes, you will have to run a timing light on it if you
want to get it exact.  I just noted where the old one was in relation to
the two bolts that hold it down and where the rotor was and inserted it
the same way.  It was close enough to fire and then I went out and power
timed it.  That is, I drove the car at operating temperature and
listened for spark knock.  If there was no knock I advanced the timing
and locked it down and drove it again; bumping the timing up, advanced,
a few degrees each time until the car knocked.  You can hear the
clatter.  Once it clattered I retarded the timing a couple of degrees
and ran it around town with the airconditioning on in stop and go and on
the freeway.  Once I was sure it would not knock I tightened up the
bolts on the distributor and it was good to go.  You get a couple of
extra degrees of timing out of the car and more horsepower.  But, if you
are running super unleaded most of the time and then get a lesser grade
of gas the engine will knock.  So, set the timing for what you are going
to run all of the time.