Can you replace brake reservoir on a vehicle?
Sure. Sometimes it's integral to the master cylinder. But some
master cylinders have a separate brake fluid reservoir that is
connected by either a fluid tube or fit into an "O" ring seal on
the master cylinder. You need to find out what kind you have and
what you'll need to replace it. If you can't find a replacement
master cylinder reservoir any other place, you'll need to get one
either from a dealer or a wrecking yard.