Generally, they're purged from sources like newspapers, but I've read depositions from court cases in primary sources, and they're usually word-for-word when possible. "Dam--d" is used frequently. The F word existed, as noted, but was not used anywhere as common as today. My presumption is that it would be used as an expression like "F---" when something bad happened, but rarely used in the "F--- you" sense, because something like "Dam--d" would be available. We also have to bear in mind that things we don't consider too shocking would have been more shocking back then. Calling someone a "scalawag," "knave" or even a liar would be insults likely to cause a fight, maybe a duel. They'd have the same provocative effect as using a very profane insult today.
