Mark

Behind the racks where the couplers are seated are two ≈1/4" copper(?) tubes joined together and bolted to the top of the antenna itself. The connection is covered with sealant.
  
     
     
  
Could this connection be corroded enough to cause bad reception/transmission of HF signals? Possible, but I haven't seen an example over the course of my time on aircraft.

It would take digging all the sealant off, disconnection, cleaning everything up, re-connection, and re-sealing, to correct an issue like that.

The "ground" side connection (or ground path) of the antenna is actually all the perimeter screws that hold the antenna to the vertical stabilizer.