Here's an embarassing one: I recently worked on the A/C in my wife's '98 Lumina. In the course of the repair I ended up having to remove the air cleaner box to get access to the low-side port; and I also removed the caps on both a/c ports.
Anyway, when I moved the car, this part was laying on the driveway:
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It's a little yellow thingy made of very soft rubber. I thought perhaps it might be some kinda seal for one of the a/c port caps (it fits on either port, but the caps won't go on with it installed).I just wanna make sure it's not something important. Any help will be much appreciated! JohnB