Hi,
My 1997 MK2 Mondeo seems to be having an issue with its driver and front passenger window seals on the exterior - just below the rubber seal there's a length of solid (ish) spongy stuff - this appears to be growing and turning chalky in places, causing marks on the windows and impeding their movement. It's also pushing the external rubber seals away from the window in places.
It's always been a problem on the driver's side but I noticed that it's finding its way onto the passenger's side. Any idea what this stuff is? Easy to fix and prevent from recurring? I've never seen this on any other car, no matter how old.