^^^ I dont think manual transmissions have water cooled transmissions. Even automatic transmissions not all are cooled by water. Sometimes they just put a heatexchanger which exchanges heat with air and not with water.
@Anup Sir,
Recently I had a look at the One-way valve design of a breather and certainly it was not a ball type of valve which we will normally consider it to be. Because I think lifting a spring loaded steel ball would require lot of pressure build up. Anyway these breathers get clogged if you were to drive it through a dirty nallah and would certainly require attention after the trip. Otherwise a clogged breather would cause Oil seals to leak.