Not knowing your cleaning practices it's hard to give you a answer. I will say that I agree with ideal tool in that the cylinder pin chamber is often overlooked and may be full of rust from past cleanings.
When it comes out on the grease you are thinking it's the grease and not the cylinder it's self.
If you use any of the subs like Pyrodex then it will cause rust overnight to form.
I would give my cylinder a good bath in Ballistol and see if the problem goes away.
SASS Frontier Cartridge class, 100% BP Shooter,