Here's what I think, guys:
Our colleague lives in New York, the climate is humid,
the green stuff is microscopic algae, exactly the same as those that live in office wotercoolers. Under the hood is heaven for them, warm and damp.
And I join your recommendations: thoroughly clean the connectors and blow them with compressed air, and then generously fill the connectors with dielectric grease so generously that it even comes out when mating. The moisture will stop coming in, the algae will have nowhere to live.
And one more thing... I would try to understand where the moisture is coming from, and the first thing I would pay attention to is the damn "trunk", the pipe that connects the air filter box to the hole in the right front fender. And I would also test the tightness of the front right mudguard to the fender.

 

Hello all .....again.....

This is exciting! It is probably the greatest mystery going on here!

First, I'll address Gearhead:
No need to apologize . I found the Ghostbusters hysterical.. (I thought my reply to it was very funny.)
Next; I hate to admit this but I only washed this car two times in the entire 15 years. I vacuumed it probably a dozen times when needed.
Car wash fluid of any kind has NEVER touched my car. (If God didn't wash it I would never believe he existed!)

To donbrew who is VERY concerned about using silicone:
I appreciate your concern. I really do, but I am always concerned about ANYTHING meltable/flammable near the engine.
The silicone i applied was at the the O2 sensor connector. I put just enough to cover where the wire enters the connector. The other place is about 8 inches from the connector on the wires close to the harness.. I put just enough there in case there to act as a block of any capillary action. Altogether I used about 4 drops of silicone.

To geg:
I am impressed that you know the difference between algae and mold. Algae always gets a bad rap because people think its mold. (This is not algae ....or mold.)

This HHR has been a Florida car for the last 8 years.

As I watched them pull out my uncle's 1932, 1933, 1947 and 1952 Rolls Royces I thought: How wonderful that these cars are being returned to England for full restorations."
Then I looked at my 2009 HHR and thought: "This car is so unique but will never last 25 years." You can't tool a part for it and it's computers are obsolete..

The mystery of the green goo ectoplasm continues....

 

The reason I emphasized the through hole in the O2 sensors is that it is where the wires are, so putting it there a) clogs the reference hole and b) can leak into the sensor side. Even the fumes can damage sensors and catalyst.
Silicone RTV is nether flammable nor meltable, after it cures. It does outgas.

 

Thank you donbrew.

To be on the safe side I will remove the silicone and replace it with a bread twisty. It's an effort to break any capillary action. (I used to tie a piece of yarn to a leaky water pipes to guide the leak to a bucket.)

Everyone here has been so attentive and pleasant. If you remember when I first posted I stated that I hated sites like these because they are always filled with people trying to "prove" something and begin arguing among each other about unrelated things. Many of those sites lose track of the person who was asking for help.

I really appreciate that the people on this site offered great advice.even if I already tried their methods. One thing I can walk away with is the idea of dielectric grease. I was told to use this by someone a while ago but hesitated because I could never find anyone that would verify it. Before I try anything I like to get several opinions. (Measure twice and you won't have to buy another piece of wood.)

All of you guys have been so kind I will try the grease and report back here in a few. If the problem persists I will take better pics to post.

 

I had a Smart car that would lose 1,3,5 gears on occasion. Shutting it off, waiting 10 mi and restarting would make it work fine for about 10 miles and it would happen again... I finally found a connector underneath that would get filled with water and cause the problem. I filled the connector with dielectric grease and plugged it back together, never had another issue. he Smart s a automatically controlled manual transmission, no clutch pedal. it was a joy to work with, too many electrical gremlins

 

Perhaps that was me in post #3 recommending the dielectric grease, I’ve used it for the last 60 years working on cars both on the road and track. There’s a lot of vibrations and moisture in a dirt modified race car, so I would apply the grease to all connections in the car, never had an issue with ignition system or other electrical problems. Any cars I’ve built for customers have not come back for electrical problems.

 

Dielectric grease is not the same thing as dielectric compound. Read the contents.

 

“Dielectric grease” is technically not an accurate term. It is a common usage term for grease with a high dielectric strength, I.e., it’s a good insulator. Such products also are designed to have a low film strength so that a good electrical contact is still achieved. Some greases (not “dielectric”) contain conductive ingredients like graphite and (somewhat counterintuitively) would be terrible for protecting electrical connections.

The same principles would apply to “dialectic compound,” a term which may be ment to differentiate it from a product intended for lubrication, which grease implies.

One common was dielectric grease for lubricating ignition points cams. But “bulb grease, is obviously not intended for lubrication, just another term for the same stuff.

I’m sure various products have various ingredients, and that the purveyors will extoll their superiority.

This comment is not copypasta, it’s just my quick explanation, not carefully edited, ‘cause I don’t feel like it right now.

 

My experience has been that dielectric compound usually has silicone in it and dielectric grease does not. I may just have odd experiences.
Dielectric grease aids in getting those many pinned connectors connected without bending the pins, as well as protecting against corrosion from leaking voltage.
"Dielectric" means insulative, it insulates just enough to stop stray voltage/current not enough to stop intended voltage/current. Way too simplified. Here is the wiki for the way too detailed explanation:
https://en.wikipedia.org/wiki/Dielectric

 

I would have to agree with donbrew