I bought my townhouse, new in 1991 direct from the builder. The fireplace came with the townhouse and is now 12 years old. Here is my problem, In the front left & right corners of the bottom of the fireplace where the floor of the fireplace and metal frame come together there is a gap of about 1/4 inch. It looks like the floor and the metal warped from the heat. It appears to me that the joints were never air tight and to me it looks like I should still be able to use the fireplace.
I talked to two fireplace salesmen and they tell I can't use the fireplace at all and it should be replaced at $6000.00
Plus. Can you help me out, can I use the fireplace? If I can't use it, can it be repaired or does it have to be replaced.

You can buy caulking tube like tubes of furnace cement. Buy one of them and fill the gaps with it. Should be tight as new or better. Easy job even if you have never done that sort of thing. If you have never done that sort of thing just buy a cheap caulking gun. You may even find the furnace cement in a squeeze tube. It also comes in cans like putty. Go with whatever you find and are comfortable with. Any hardware or home center should have the stuff.