A systematic optimization of the components of our polarized electron source has markedly improved its long term stability over earlier versions. The major factors shortening the lifetime of the source have been identified. The essential parts of the spin polarized electron source, such as the vacuum system, crystal holder, cleaving mechanism, caesium dispenser, oxygen admittance tube, and computer control activation features are discussed. The lifetime of the source now exceeds 500 h with a constant polarization of 28.5&percent;. ©1997 American Institute of Physics.