Freon is a Trade name, but it does not designate R-12 .. It is Duponts
tag on all their CFC refrigerants .. R12 just ONE of their Freons.

.. but it is also common to see freon/refrigerant interchanged in the trade , along with ' ya need a shot of gas '..

But, Refrigerant is correct.. and adding some refrigerant w/leak sealer is not a recommendation I would agree with.