Got to work this morning and had to get something from the passenger side... when I noticed quite a bit of something leaking from the rear end of the running board!
Pretty much knew what it was going to be, but I was just surprised it had made it so far!
Damned drain. Gave it a squeeze from under the dash and it let quite a lot flow through, but I think I'm going to need to try and remove it to clean it properly. Poking from underneath hasn't sorted it previously apparently!