Body (1) is the imported solid body you started with.
I assume that this was a solid body and not a sheet body. On a solid body the exterior faces are enclosing a volume, there is logic connecting the faces such that the solid modeler "knows" that it's "watertight" , The volume can be calculated by a single click.
A sheet body might be enclosing a volume but the solid modeler regards the sheet body as open, the edges have at least one opening. the volume can only be calculated with some manual assistance.
The Unsew feature i see in your feature tree should not be needed.
If the Body(1) is a solid body, we will be creating a "knife" by the extrude and the planar surface plus the sew feature.
then that "knife" can cut the shaft from the housing. You will after that operation have three bodies, two solid bodies and one sheet body.
If you remove the parameters of the shaft, that will be renamed into "Body(3) and you can then delete the "knife".
remaining : body(1) and Body(2)
Search for "Remove feature parameters".
Regards,
Tomas