Hi all had the problem of a few drops of water on rubber mat in passenger footwell a few weeks ago found out what it was and want to share the fix if your car has roof rails inbetween both ends of the rail there is a rubber fillet slotted into the groove this is just stuck in with double sided tape take this off and you will just have the slot left this will have like sticky tape in with a chisel remove this and on my passenger side you will see about in the centre a single phillips head screw in my case this was loose so silacone it and the rest of the groove and replace rubber fillet this stopped my water coming in the screw was for holding a little cable clip under roof lining thanks all.

nice little tip that, no doubt save others hours trying to find the leak, good on you.