I had that problem once awith some wet carpet and tried to work out where it was from. It only took me a few minutes to realise that Id left the window open an inch on the drivers side overnight - letting in all the rain water !
So I guess you would have checked that the window was closed ?
Had a quick look tonight before it got dark. Stopped the hood etc half way open and could see the carpet behind the shelf wall was also wet, and then soaking through to the cockpit itself. It's a small area, but quite damp. Also looks like some had gone down the bottom of the hood strut. Just got to work out now how it's getting in