Try the different flints first as suggested.
Also, every lock is different. The big question . . "bevel up or bevel down". Most install their flints with the bevel up. However, every once in a while, a lock seems to work better with the bevel down - install one that way, take a look at the geometry of the lock and slowly release the cock and see how it strikes on the face of your frizzen.
I don't have any experience with the lock you are using but I have had experience with L & R - they have always proven to be top notch.
You don't state how old or how "used" your rifle is either. I am assuming that the face of the frizzen is in good shape?
If you're not getting a good shower of sparks in to the pan, I'd look at the flints first. As already stated, they don't last forever. You can knap the edge and sharpen it some which will extend the life of it a little. If you've ruled those things out, then make sure that the face of the frizzen is hardened like it should be. If not, it can always be rehardened with Casenite. Years ago, Dixie used to carry this just for this purpose.
If you've ruled all of these things out and have your mind made up to replace the lock, I'm sure you would be happy with a L & R. They are good quality lock and good folks.