uberti 1851 navy and over time I've had to replace some parts
That is most puzzling. They are very simple, very study mechanisms. There is not much that can go wrong with them.
Single actions are not complicated. I suggest you take it apart look for parts that might be broken and order replacements. On reassembling simply stone all edges and especially surfaces that touch other parts.
IMHO, $100.00 or more to tune up one of these is, in diplomatic terms, good business if you can get it.