I would like to add this advice for those who have the later vented opti:
It is possible for the neoprene vent line (runs from front of intake manifold to opti, and then out of opti to the engine air intake). to be crimped closed if one is not careful when replacing the water pump or the opti itself. I found that a GM dealer allowed the air line to be crimped closed between the rear of the opti and the front of the intake manifold when he reinstalled the water pump after replacing my first opti. The dope reinstalled the old leaking water pump back on top of my new opti. Can you believe this?! This crimp prevented the vent line from purging moisture from the Opti so when the water pump continued to seep the Opti sucked in the moisture, retained it well, and corroded itself all to heck with copper sulfate-looking crap. This is the result of:
1. Moisture intrusion in opti.
2. High voltage arcing around antifreeze vapor in opti.
3. Lack of fresh air circulation due to the pinched off vent line.
4. An idiot or disgruntled Vette technician.
I encourage all vented opti owners to check the vacuum on that line!!! To do this find the intake side of the line. You will find it attached to a grey plastic "L" inserted into the neoprene air intake neck (the black ribbed thingy connected to the rear of the air filter housing;you know!). You will not be able to detect a vacuum with your finger, nor will you hear the vacuum because this vacuum is significantly reduced by a couple of blue/white plastic reverse flow air valves located in line with this vent line. These are to prevent this otherwise full-on engineered vacuum leak from causing... well, a significant vacuum leak (ie-a lean as heck mixture). This sounds like a put-on but it is true: carefully bend over the intake thingy and place the tip of your tongue (no kidding; trust me!) on the end of the vacuum line. After a few seconds you will begin to feel this very light sucking action on your tongue IF the vent system is working correctly. If you feel no vacuum you either have a plugged vent line or you forgot to start the engine dummy.
Gawd, I'd love to see a picture of one of you guys performing this tender-loving act of kindness on your beloved Vette.