As Bull3450 pointed out, the barrels back in the 1700's and 1800's were not made of the steel that they are today. They were wrought iron and hammer welded which resulted in a mild steel. As such they were much more subject to rust than modern steel barrels and proper maintenance was even more important then.
galamb came up with that great primary documentation from Christian Oerter in 1773 pricing his rifle at 8£. That was about 3 times as much as a trade gun, fowler or musket. I have often seen quotes that the price of a rifle was almost as much as a years wages for a man of the times. I can quote from the payroll records of Herrick's Green Mountain Rangers in 1777 that each of the Rangers in Captain John Warner's company were paid 1£ (one pound) per month and those were considered good wages. So 8£ would have been 3/4 their annual income - comaprable to buying a new car perhaps?
Keeping in mind that it costs so much of their yearly income to purchase the rifle, it is very difficult to believe that they would neglect to properly maintain it. It was not only the most expensive item they owned, their safety and livelihood depended upon it. Leaving it loaded for a few days at a time caused little problem because the fouling of burnt black powder is where the corrosive problem comes from. Certainly in the field by yourself in hostile territory, cleaning your rifle might not be at the top of your mind. However, when in a group of men, cleaning your guns/rifles in rotation makes a lot of sense.
Despite the earlier quote that the British troops were not allowed to remove their locks, they were required to clean their arms. Removing the locks resulted in lost parts, improper assembly, and malfunctioning weapons, which is why they were forbidden to remove the lock. They still had to clean the the outside of the lock (pan, frizzen, cock, touch hole, etc.). In fact, each British soldier was required to clean his arm and polish the metal with a paste made from brick dust (doesn't work with modern bricks). They could be court martialed if their muskets weren't bright and shiny at inspection each morning. So they cleaned their muskets every day.
It would also be good to remember that there were none of the common conveniences in the 1700's and 1800's. So, no internet, no TV shows, fewer books and relatively little to do after dark on the frontier - perfect time to clean your gun.
One advantage that we don't have now is that both whale oil and bear oil/grease were widely available. Both of these protect steel and iron surprisingly well and are also good patch lubes. A friend of mine rendered some bear oil out of bear fat (a laborious and smelly process) and used it on both his barrel and lock. He never had even a tiny bit of problem with rust. He was showing his rifle to me at a reenactment a week after he had applied it to his rifle and it looked like it had just been freshly oiled. So some of those commonly available substances were more than up to the job of protecting and preserving their flintlocks.
I think it's a mistake to presume they used less care with their firelocks then than we do now.
Twisted_1in66 :thumbsup: