Nissan Repair: 94 Sentra 1.6 manual transmission, light flickers, oil contamination

Question
Mr. Von Sudderth:
Thanks for your prompt reply.  I removed the distributor and took it apart to the point where I could see the speed sensor.  There was no sign of oil contamination.  I DID see a small amount of oxidation on the housing next to one of the rubber plugs.  I thought that it may be possible that some of this oxide spalled off an clogged one of the windows, but really doubt it.  I cleaned that off and blew it out with dustoff.  Do you have any other possibilities?  I forgot to mention previously that the fuel pressure is right where it's supposed to be.

thanks once again,
Roger
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The text above is a follow-up to ...

-----Question-----
I have an intermittent problem.  On the highway, the car bucked once.  About one or two minutes later, it bucked again.  Then, within about 15-30 seconds, it continuously bucked for several seconds until it seemed to completely lose power.  I pressed in the clutch then let it out and all was well.  During the bucking/power loss, the check engine light flickers, comes on, then, when I regain power,it goes out.

My daughter uses this car principally.  She has had the problem around town as well as on the highway.  She gets gas from several different stations.  After the last fill, she drove the car back to college (~35 miles) without a problem.  I went to pick it up a few days later, put some dry gas in and drove it home.  No problem.  Drove it to work the next day ~ 20 mi.  No problem.  Drove it home, had the problem once.  Drove back to work the next morning, had the problem again.
Other info.
New Plugs & wires. Cap and rotor are about a year old.  MAF is new (rebuilt).

Any insight would be helpful.
thanks,
Roger
-----Answer-----
Roger,

Sounds like your distributors optical pickup, receiver and shutter wheel are contaminated with oil.  The internal seal in the distributor fails with age, ten years or more, and oil makes its way up to the optics.  A rebuilt distributor should solve the problem.  My daughter's Stanza did the same thing...

Answer
Roger,

Then you would want to get a volt ohm meter and check the coil and the transistorized ignition module that ties to the distributor.  A Haynes manual will give you the readings to let you know what is good or defective.  Oh,
check to make sure the air intake hose from the MAF to the throttle body is in good working order.  No cracks and the clamps are tight as unmetered air will give you similar problems.