Every time it rains I get water pouring into my passenger (Left hand) footwell via the gap in the trim where the ODB2 Socket is.

I've had the pollen filter out on that side and it's dry at the front (ie: the end nearest the removable cap / cover) but wet through at the back (the end buried in the car).

Before I start taking the trim apart on the bottom of the windshield, is there an obvious culprit here?

You need to go lower than the pollen filter there is a rubber gasket that fails
also the screws at the top screw into square plastic pieces and the small square gasket on these fail

tarphenry said:

You need to go lower than the pollen filter there is a rubber gasket that fails
also the screws at the top screw into square plastic pieces and the small square gasket on these fail

Click to expand...

A blob of silicone round all the screws and a bead of it along the top of the pollen filter cover usually fixes it.
Also a blocked drain in the plenum will cause the same problem.