However, Rolex has a right to be against that if the part that you are trying to replace is a part that is needed for security.
Think of it like this:
Rolex makes their watches free so you can get one and try it out for a few weeks. But they make their watches so they need a specific part in order to keep working after those few weeks are up. They do this so they can make sure that any watch they provide this part to is in a fit state. After all, they don't want someone to get an old tatty watch that's all rusted, put this part in, and then claim that the Rolex watch they just purchased is a bad product.
So Rolex decides, "We'll make it so that if people buy a watch from us, or from an authorized seller, we'll provide the part they need to keep it working. After all, if it's purchased from us or an authorized seller, we can be pretty sure it was sold in good condition. But if it was purchased from anyone else, we have no way of making sure that the quality is good enough, so we won't provide the part."
And if someone gets a really old watch that doesn't have the part, and asks Rolex to provide the part, Rolex has every right to say, "We haven't made that model of watch for ages. We don't make the part you need anymore, and even if we did, there are no authorized sellers who are selling that watch anymore. So we can't help you out."
And then they'd point at all the new watches that can be purchased which do not have this limitation.