One of the cool things about working on muzzleloaders is the learning curve. If you send it back, you'll never learn anything.
Here's what I'd do. I'm thinking that the timing of the frizzen is out, and that this may be caused by a frizzen spring that is not balanced with the power of the mainspring. Put the cock at half bent, and close the frizzen onto the pan. Raise the frizzen slowly and watch where it flips open under the tension of the frizzen spring. The frizzen should snap open by itself when the back bottom edge reaches about 3/8" off the pan. If it does not, and the toe of the frizzen is polished as well as the top of the frizzen spring's leaf where the contact is made, a couple of things can be done to improve it. Reduce the thickness of the working leaf of the frizzen spring by filing it thinner over it's whole length, and then re-polish it. Do it a little at a time, returning the frizzen spring to the lock for testing, each time you make a change. It may take a number of tries, so be patient and keep at it. When the frizzen spring is balanced in power with the power of the mainspring, the lock should work much better.
Experimenting with Siler locks to eliminate that problem, and/or just tuning to improve the lock's speed and or function, I have also removed the frizzen spring, and heated the tip red and bent in downward just a little, right at the point where the frizzen should trip over and open by itself. This is a little trickier, and you need red heat, so the spring must be altered, re-polished, hardened and tempered each time you make an adjustment. But I have radically improved lock time and removed frustration doing this, and learned a whole bunch of stuff along the way. Tuning flintlocks is a lot of fun, and making it better is very satisfying.