Originally Posted by Army

This is your W123?

It looks like it but I thought I'd check... I think that that's the floor pan. Lift up the carpets and remove the sound insulation to see the extent of the damage.

Some where like the front windshield or the pockets into which the bonnet hinges retract will be leaking. Water falls down into the footwell(s) and flows along the floor pan (trapped) between the sound insulation, the floor pan, and that wonderfull rubberised MB undercoating that makes sure it all stays there until the metal has rotted away.