Well, I have never had a flinter, but it's a fairly simple mechanical device. If the mating surfaces are not planar with one another then they will not make a good seal (of course). Check to see if a part is bent, or perhaps some parts need to be filed to make a good fit.
Steve
Yup. I good lock, like any of Chambers, will not have this problem. I've seen them fire upside down, though I really have no reason to try that myself.That is one of my pet peeves about some of the "over the counter" flintlocks. You should be able to hold it upside down, shake it, whatever and not lose any prime.