Just my opinion, but if you do replace the nipple it should be steel, not one of those obviously new Ampco Metal (bronze) nipples.
The Ampco nipple is a turn-off to me as a collector. Not really a big deal itself, but it indicates lack of thought in restoration & causes me to examine the rest of the gun more closely.
An old nipple would be nice, if you can find one.
No nipple at all? Hey, this gun hasn't been messed with ("Improved") by some collector. I want THAT one!