  We argue that surface spin and thermal conductivities of three-dimensional
topological superconductors are universal and topologically quantized at low
temperature. For a bulk winding number $\nu$, there are $|\nu|$ "colors" of
surface Majorana fermions. Localization corrections to surface transport
coefficients vanish due to time-reversal symmetry (TRS). We argue that
Altshuler-Aronov interaction corrections vanish because TRS forbids color or
spin Friedel oscillations. We confirm this within a perturbative expansion in
the interactions, and to lowest order in a large-$|\nu|$ expansion. In both
cases, we employ an asymptotically exact treatment of quenched disorder effects
that exploits the chiral character unique to two-dimensional,
time-reversal-invariant Majorana surface states.
