Green coloured liquid in passenger footwell! HELP

[zakh]

hi members,

over the last several months ive had a really funny smell in my car, ok its not me! lol
but seriously its almost like a sweet smelling fungus smell. anyway today i was cleaning the inside and i removed the passenger carpet lining and i found this dribble of green liquid...
my car is a 1990 190E with air con.
My question is, what is this and what do i need to do to solve it!??

many thanks in advance