I would suggest you read my first response again. I am not disagreeing with the cleaning crowd, but you do pick the hole so I doubt fouling is the issue. If that channel is much over the .035 length, that is your problem. You can solve that by deepening the cone on the inside, but enlarging the flash hole is not necessarily a good thing. Too large of a hole will allow some powder to be pushed out when you are pushing the patched ball down. Now there could be fouling issue inside the chamber, especially if it is a poorly made Patent chamber with rough walls, but I think you indicated this is happening after only a few shots and I suspect that fouling is not the culprit.
I believe your liner is set too deep, giving you somewhere around a .075 to .095 (maybe even more) depth in your spark channel. If so, you will experience exactly the problems you are describing. You will have to destroy your liner to get it out or pull the breech plug to access the inside of the cone. It is easier to remove the liner and install a new one. If you want to use that style - no problem. Open up the inside cone a little before installing it and you can stop short on the installation and peen over the face to seat it in the chamfer ring.
You can also cone the outside of the liner some to get the same effect as deepening from the inside. If you want to see if the channel depth is really the issue, try coning it on the outside before you do anything else. If that works, leave everything as is and have a good time shooting. There is nothing wrong with having a liner coned from the outside. Try to end up with the .035 or so channel. It is practically impossible to measure it (installed), but you can eye ball it pretty close. I have used a 82 or 90 degree counter sink for this before and also solved the problem. If you use a counter sink bit, be careful about opening up the hole diameter. 1/16" is the magical size. You can use a appropriate sized drill bit as long as you go slow and keep it from wandering around the liner face. You don't want a cone the size of the hole face of the liner - maybe no wider than 1/3 to 1/2 the diameter of the face.
Also, it has been proven that priming away from the flash hole is a bad thing. There is plenty of testing and evidence to back that up. The last issue of Muzzle Blast and previous issues have covered that extensively. I suggest you fill the pan up (or close), close the frizzen and tap the side of the lock to make sure it is spread out across the entire pan. If you don't want to use that much priming powder, stack it up against the touch hole. More priming powder allows for more area to catch a spark and then more sparks to go their merry way. I pick, prime the pan full, close the frizzen and give it a little tap to get powder over to the touch hole and maybe even in it. If I have the rare misfire, it is because my flint is dull and my priming powder does not ignite in that senario.
Edited. Well, I tried and good luck but it fired the first few times and then did not. That is not water/oil inside your chamber.