  A precise characterization of the recently discovered crossover to
hydrodynamic transport in electron liquids, and in particular of a conjectured
exotic odd-parity transport regime, requires a full solution of the
Fermi-liquid collision integral at all temperatures beyond state-of-the-art
analytic leading-logarithmic approximations. We develop a general basis
expansion of the linearized collision integral applicable at all temperatures,
and employ this to determine the decay rates of Fermi surface perturbations in
two-dimensional electron liquids. In particular, we provide exhaustive data on
the decay rates for a new odd-parity regime, in which parity-even Fermi surface
deformations decay rapidly but odd-parity modes are anomalously long lived. We
find that this transport regime exists at fairly large temperatures $T \lesssim
0.1 T_F$, putting this regime within the reach of current experiments.
