Imported 3D Soild has missing faces - causing issues

I've imported some 3D models from an online library and several of the parts have fillet faces that are 'missing'.

SW cannot heal the face(s) and its means I cant combine or use the 3D part properly.

Is there a way to fix this kind of problem. I've tried several methods but I've not had any success.

I've attached a very simple part to show the problem. Other parts are much more complex & would be extremely difficult to re-model.

Thanks.

SolidworksModeling And Assemblies