Fireplace repair, gasket or cement?

[farmguy]

Hello all, new here.
I have a Vermont Casting winter warm system and I am currently replacing the cast iron side of the unit. I have removed the top and right side (the cracked side) and in the process the left side and back is a little loose and it was assembled with furnace cement(?). So my question, do I need to go ahead and remove the remaining side and back and reseal/rebuild the entire unit or can I just do the pieces I have off?

And a second question, what is the difference between gasket cement and furnace cement?

....yes, I'm a rookie at all this...

 

[begreen]

Welcome. I'd take it all apart, clean joints and then reassemble using furnace cement per instructions on the seams. Furnace cement is much thicker and more spreadable than gasket cement.