I'm not sure what you're looking at, but I'd call a furnace tech out to look for the source of the smell. It might just need an annual cleaning.

Gasket cement can be used for minor cracks.

Need the exhaust flue checked though, ensure no obstruction.

Vith thank you. The cracks look like a hard boiled egg that's been cracked with a large crack and smaller ones branching off. No pieces are missing. I'll thae the flue checked as well. Thank You