Wet rear seat and foot well

[Dingo1963]

Have a BA and last night drove in torrential rain for 6 hours. This morning I noted the wet carpet in the right rear passenger floor mat. Further investigation identified very wet rear seat bench on right side also.
A check under the car/wheel arch, did not identify any obvious entry points for the water.
The car does not leak if just sitting in rain.
Anyone have this happen, if so what was the fix?
Appreciate member feedback.