Complex sentence: Due to the fact that some of the stations have been operative for over four decades, as well as neglect caused by the lack of funding during the 1990s, most of them require a major facelift and some severe repairs on hydroisolation and structure.
Split into simpler sentences: Due to the fact that some of the stations are already four decades into exploitation as well as neglect caused by the lack of funding during the 1990s. Most of them require a major facelift and some severe repairs on hydroisolation and structure.