I'm going to change my rear and front differental fluid. When i take the case off and after draining the fluid and scraping away the old gasket, do i have to buy a new gasket for it or can i use gasket sealer out of a can?

You can just use some RTV Sealant. No Need for a new gasket and most places won't have a gasket for it anyways because there no need for one.

Alright ill do that. Thanks.