We live in a late 1920s house. For here, that is on the historical list and we get a tax break on it. There is an incentive to keep stuff "old".
We have hard water and no water softener (never-mind why).
Normally - I hire a plummer.
But I do valve stem replacement and cleaning from time to time.
I found I can soak the stems in CLR and that breaks stuff up a lot. For assemblies I use an electric toothbrush dipped in CLR.