My first/current/last one was bought by my father sometime before decimalisation - it's still intact. Doesn't see much use though - I tend not to cut myself.
I have had my current pencil for roughly 4 years with no breakage.I haven't dropped it though so I think that helps
My latest alum block suffered an internal crack after I ,rather heavy handed, dropped it onto the sink from 6 inches height.
The odd occasions I want to use mine, I dip the tip off the styptic, hit the spot I need to hit and blot the styptic dry on some toilet paper, then leave it "open" to dry.
Typically the styptic pencil is made up of aluminium sulphate (soluble) and talc (insoluble), compressed together - add water to that and it will partly dissolve.
If it's kept wet (by not drying it and putting it away) then the moisture left will slowly permeate through it and weaken it.