I have a sewage ejector in the basement (above ground) and it is starting to smell. Is there a gasket of some sort uder the lid? If so where would I get one? Does anyone know why else it would smell?

Yes, there should be black, thick and sticky, one piece gasket under the lid. Also, there should be rubber gasket around each pipe and cord penetrating the lid.

Identify the manufacturer and go to their web sit to purchase new set of gasket for your system.

Question: is there a vent venting the sewer ejector ?

Back to you. Milo