I've been trying to find this out too (for a mark III Golf). The smell's more noticeable in heavy traffic, I sometimes see smoke coming out of the air vents when the air's not switched on, and find condensation on the windscreen.
It seems to be a problem with the cooling system. The coolant leaks onto the engine where it's burnt off. Maybe the heater core?
Bad heater core.
heater core leaks
Rubber is not a plastic.
Leaking valve cover gasket.
plastic is harder than rubber
the rubber elbow is a drain for the heater and ac box, it should only have clear water coming out of is on a hot day with the a/c cranked up. and antifreeze indicates a bad heater core.
plastic is better than rubber
It is a drain tube for the pan housing the heater core. If the heater core leaks it will go out that pipe instead of inside your car.
Rubber will bounce higher than plastic because the rubber has more elastic qualities. A rubber ball will give a little when it hits the floor and a plastic ball will not.
I don't think that there is any rubber or plastic in Hubba Bubba.