My situation likely involved coolant...which in my case is green likely contributed to the "green slime" coming from the opti the one time the dealer showed me the inside of it (weeping WP). The two Opti replacements they did after (one at 1200 mi and the other at 500 mi) did not have any "liquid" inside them but the terminals and rotor tip did have flaky crud (IIRC greyish black) on them. After I put the check valve back on the short life span of Opti's problem went away.

And after my warranty ended I swapped the then 500 mi old AC Delco weeping WP to a EWP. That was 17 years ago.

I may be using the term "oxidation" incorrectly but "crud" does build up inside Opti's that are not vented.

Again, since the OP says his Opti is missing the vent harness, that "may" be the core cause of his problem. And yes it could be the optical sensor itself or something in ignition outside the Opti itself.

He will only know after he opens the Opti up if "contamination" exists inside Opti

 

The MSD opti Arrived today, The car is alive. The opti was the Original one (1996)!! I don't know how that survive 1 year with out Vaccum lines. Apparently water destroyed it!!

 

Glad you got it sorted out. Did you happen to open it up and take a look inside?

 

Yes, I open it! There was a lot of moisture and a Yellowish stuff