Is it the Water Pump?

[Cunningr]

I had same issue this summer. The overflow is in that spot where you described. In my case the service was accomplished in Oct and the overflow occurred in Jul, I live in southern spain temperature was over 100 f that day. When I looked at the level it was above the max line, after checking it several times I came to the conclusion that it was to much fluid do to expansion and so it was over flowing the excess. Happened several times the shop couldn't find any issue, and the car always maintained normal temp when driving. To make long story longer I think I opened cap to check the level didn't get it back on correctly, saw over flow panic sets in, shop cant find a problem. Then I keep checking causing it to overflow about ever other look until someone on the list mentioned the cross threading.

The other issue could be a crack in the reservoir see if you have any fluid in the trunck under the matts.