Two series of diffusion coefficients D are reported for the triethylamine-water binary critical mixture. One has been obtained from quasielastic light scattering measurements, the other one has been derived from broadband ultrasonic spectra, yielding the relaxation rate of order parameter fluctuations, and shear viscosity data. Using high frequency shear impedance spectrometry in the range 20-130 MHz, relaxations in the background part of the viscosity, resulting in viscoelastic mixture properties, have been found. Both series of D data agree either if a half-attenuation frequency distinctly smaller than the theoretical value Omega(1/2)=2.1 is used in the Bhattacharjee-Ferrell scaling function or if the viscosity extrapolated from the shear impedance measurements to low frequencies is applied to the Kawasaki-Ferrell relation. This extrapolated viscosity is smaller than the static shear viscosity measured with capillary viscosimeters.