To my knowledge
Nobody has ever had to change a mater cylinder for this fault
Years ago both they use to get changed as the fault wasn't so well known
I would just confirm it with grease
Then just changed the faulty part, as per video
10 minutes it's done, bit longer if you not done one before, several people haven't even bothered changing them, just regreased, without out any further issue
The only master cylinders I know that's confirmed to be faulty (not changed as a precaution) are on the 500 that leak into the drivers foot well
There's literally thousands slave changed on fiat and ford forums, two people on here have done at least 7 between them
Correct part can be difficult to obtain, it was out of stock everywhere for months last year, there is an alternative that's known to work if needed