We investigate spin-polarized electron transport through ensembles of nanometer scale Al grains connected in parallel, at 4.2K. We demonstrate spin-valve effect and the Hanle effect. The tunnelling magnetoresistance (TMR) depends strongly on current direction, which we explain by comparing spin-coherence time T2 and asymmetric electron dwell times. TMR decreases rapidly with bias voltage, suggesting that T2 scales with electron-phonon energy-relaxation time, analogous to the Elliot-Yafet relation in bulk metals. This leads to an estimate T2~0.6ms, which tells that quantum computation could be feasible at 4.2K.