Nipples do wear out, how soon depends on a few factors like the powder type, the size of the charge and of course cleaning and care.
Hot sporting grade powders and large charges lend to what's called "Gas Cutting".
All that pressure from the charge going off, hit's the nipple hole too and there's always a small amount of gas leaking out in reverse of the muzzle and going out the nipple vent hole.
Signs that the nipple needs replacement;
If your a target shooter the groups will begin to open up, pressure is working out of the nipple vent leading too a variable in the pressure pushing the ball.
You know it's getting bad when there's enough pressure coming out the nipple vent that it pushes the hammer back to half cock, actually by the time it's doing that your groups have suffered for some time already or it may be the cause your not getting a tight group to begin with.
I go through a couple nipples each shooting season in my 54, I use T7 and a stout load.
250-300 shot's and the nipple is toast for target work.
If your gun is second hand it's a good idea to replace the nip so you know it's good. If it's a TC factory or GM factory nipple it was junk when it was installed at the factory.
The best nipple is; well that's as varied as guy's tastes in vehicles they drive,
I've had good luck with and prefer Knight's Red Hot, but again I use T7,,
Spending $5-6 on a nipple 2-3 times a year doesn't bother me in the least.
I tried the Ampco Bronze and the vent hole is too small for reliable ignition with the Faux powders.