I read your STEP file into SpaceClaim. I combined all the bodies back into a single body. On the Repair tab, clicked the Inexact Edges tool.
It found six, but could only repair four. Two inexact edges remained. This may cause problems meshing.
Also, I can't remove this extra face.
Precise geometry is needed for easy meshing. Inexact edges are going to deliver poor quality meshes as I found in this trial below.
It might be worth building this geometry from scratch in SpaceClaim. I did a blend instead of a chamfer and used a sphere to slice out the joint. The parasolid file for that is attached in the zip file.