  We systematically study the coherent transport (Josephson tunneling and
counterflow current) and its breakdown which leads to incoherent charge flow in
in the excitonic BCS condensate formed in GaAs bilayers at $\nu_{tot}=1/2+1/2$.
The Josephson currents in samples with three different interlayer distances
vary by four orders of magnitude. In contrast, the breakdown thresholds for the
$\nu_{tot}=1$ quantum Hall state are comparable. Furthermore, Coulomb drag in a
Corbino ring reveals that the coherent counterflow current coexists with the
dissipative charge transport.
