A couple of weeks ago, I checked my coolant levels in my 2013 Volt. I guess maybe I put the cap back on without tightening it or something, because I opened the hood today to refill my washer fluid and noticed the coolant cap was gone. It is the coolant reservoir in the back on the passenger side. Attaching a photo for reference. I found the cap on gmpartsdirect for $7.97 so no worries there, but should I be concerned about contamination of the fluid in the system after driving without a cap for a few weeks? Do I need to get the system flushed asap? Levels look okay, so I didn't lose any from sloshing around.