I am sure that happens (Watchmakers within the Rolex network fitting aftermarket parts to Rolex watches), but I think it is far more the exception rather than the rule. For decades, Rolex has prohibited the installation of non-Rolex parts in their watches. In fact, there have been numerous court cases over the years brought against Rolex by indy watchmakers or consumer organizations in efforts to stop Rolex from restricting their ability to engage in 'free trade' on behalf of owners & customers. To the best of my knowledge, none of these types of cases have been successful. So if 1 of your indy's customers even happen to have another Rolex watchmaker work on their watch (likely), at the very least, he would lose his account. At least, that is the word I hear from reliable sources within the network.