[Cunningr]

I had same similar issue last year, never found a leak or reason for over flow other than the mechanic had the coolant serviced to just under the max line. My guess was the coolant was serviced in wither and maybe the giant difference in winter to summer temp here caused the excess coolant to over flow, as soon as it was a little below the max line never lost any more fluid. The other possible was the cap crossed up, from me checking the fluid.

Anyway hope your good to go!