I have chased pan fit endlessly on some locks, now if it doesn't leak 4F I am good with it.
I have an old Gustomsky lock that has the frizzen screw hole drilled wrong and an arm that won't allow repositioning of the hole. I finally gave up on getting this frizzen to seal the pan.
The above pan fit is so bad 4F drains out of it like water, this cost me a turkey one time. I walked in and set up over my decoys, I had instant gobbling to my call and forgot about my leaky pan, I had primed when I left the truck. 5 jakes came running in, as I had not killed a turkey with a flintlock I was't choosy. I drew a bead on the largest one and dropped the hammer, nothing happened, the click of the hammer caused a panic in the flock. I re-cocked and tried again, nothing, I flipped open the frizzen and found the tiniest pit of prime left in the pan. By now the turkeys had taken wing, I tried a 15 yard wing shot on the last one, the gun hang fired but did go off, I shot the air behind the turkey.