My flintlocks have always been reliable for me. I hunted moose one year in northern Ontario, it rained so much my tapered ramrod swelled up and I couldn't get it out of the pipes. Luckily I had an extra rod with me. I checked the powder in the pan frequently and if I thought it was damp I changed it. When the time came for my chance it didn't let me down and I killed a big bull moose.
At night I keep the vent pluged with something. Also in damp weather I sometimes poke a little 4ffff into the touch hole. Percussion guns have failed to fire for me a few times but if you do your part a flintlock will not let you down.
Here's a little poem I wrote a while back
"Flint be sharp to make good spark, no damp be in the pan
pick the vent it must be clear to do the job at hand.
plug the vent with feathered quill when storing for the night
do your part so carefully and it will serve you right."