What causes this?

[drakon543]

Yes. AC Delco or Delphi. The aftermarket caps leak........

Also, I suspect out-of-spec screws that come with the aftermarket caps contribute to the distributor base cracking around the screw holes.

And, AC Delco or Delphi on anything electrical or electronic such as sensors. Other manufacturers are a bit of a crapshoot.

i haven't had any problems yet with anything else. dealt with the dizzy crap long enough and its not my first gm so ac delco or timken wheel bearings. outside of that it hasn't given me a problem.