If its a heater coolant leak you'd know it. It reeks.

More than likely a blocked drain.

Run the car up on some ramps and have a look for a hole/hose near the transmission tunnel, roughly under the dash area. If you can run a piece of wire or electrical cable up and down it a few times, not too far, and get out the way. Better still if possible use compressed air, but not a full blast otherwise water will spray around the dash/electrics of the car.

Its an easy fix but you will need some special tools:

A long weight

A tin of compression

Two skyhooks

Some rainbow coloured paint

A set of metric adjustable spanners

A left handed screwdriver

and a tin of scotch mist

you had better add a 6" snatch reamer to that list too