Complex sentence: Conservation best practice however is to retain old mechanical clocks because they are part of the fabric of the building, and in most cases will outlive modern electric replacements: however, even older clocks are not necessarily wound by hand any more.
Split into simpler sentences: Conservation best practice however is to retain old mechanical clocks because they are part of the fabric of the building, and in most cases will outlive modern electric replacements. Even older clocks are not necessarily wound by hand any more.