Woody, there is no reason to do this. These joints are tight and taping the joint at the motor plate will make it a real pain to disassemble the unit should you ever want to do that. But not a problem, other than this.
If the impeller is spinning in the correct direction as shown by the arrow decal on the housing (watch it when it spins down), the only other potential culprit I can think of is a leak somewhere at your dust collection barrel (lid, joint, barrel walls). For many people, this has been the source of their problems. But, you say you don't see any air movement at the joint of your barrel and it's lid and presumably your barrel is itself air tight.