I would certainly recommend checking all four corners and everything in between before replacing the master cylinder. No problem with replacing it, just make sure you have identified the real culprit. Afer all, your goal is to get the brakes fixed, right?

You might actually discover that nothing is leaking. The pads could be worn to the point that the master cylinder has sucked air and all you need is to replace pads, change the fluid, and bleed the system.

230/8