A well known example that creationists latched onto was the bacterial flagellum, insisting it could not have evolved, as removing any part would mean it cannot function. However there are thousands of different flagella in bacteria, which vary considerably in form and even function.
The best studied flagellum, of the E. coli bacterium, contains around 40 different kinds of proteins. Only 23 of these proteins, however, are common to all the other bacterial flagella studied so far. So contrary to creationist claims, it is possible to make considerable changes to the machinery without mucking it up.