Heater matrix or something else

I wonder if someone could give me some advice I'm not to sure but I think I may have a leak on my heater matrix on my Audi 80 cabriolet 2.3.


When I put my heater on hot I get a smell of antifreeze from my heater and what looks like smoke coming out the vents for a split second, also the car doesn't seem to use water but it has had some air locks which when I take the cap off the expansion tank the gauge goes back down to zero and wont go back up again and the anti freeze level seems to also go up a tad.


Also I've noticed that the vent knob which directs air from the screen and footwell doesn't go all the way round and wondered if this was related.


I was thinking if it has a small leak on the matrix could I use k seal without damaging the car.


I'm hoping that its more to do with the car being standing for months that's caused this but maybe I'm being to optimistic.


Any suggestions would be appreciated

Their is a very old leak, dirty stain which was dry which I steam cleaned out of the carpet when I first bought the car 6 months ago which looked years old, but nothing has come back.
Also it looked as if the centre console and vdo gauges had been removed in the past.
I haven't used the car for a few months and just wondered if maybe moisture had got in the car as it has been sitting on the drive for a few months.
But I think I'm just trying to kid myself there's not a problem.