I hate to get all technical and s**t at this point but the bond to the metal will be enhanced with a bath in MEK, acetone, or Lacquer thinner. It isen't the JB I would worry about failing as much as the substrate bond.
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Paint the little dobble to match and rock on!
If ya coat that there JB Weld with Kreem tank sealer it will reattach a broken float support post that has been drilled and pinned also and save unstacking the rack.