Cannot see any reason to suspect your master cylinder.

I have done that job, it was not difficult, just tedious. As others have said:
Soak with P Blaster or good penetrating oil beforehand
Use a good quality wrench.

Try not bend the lines too much and change their angle to the block, this will make it harder to get them started in the new block.

Be carefull not to cross thread when starting the threads, not all the lines will start easily.

Better to pressure bleed if possible but you should be OK to bleed using the master to pump because it is fairly new. An old worn out master will often fail after using to pump and bleed the system.
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David Hunter