IMO, unless one shoots very high volumes(+1000 shots), it’s unlikely that stainless, or even modern steel non-liner barrels will wear out with proper vent-hole picking and cleaning procedures. There is a fundamental difference between the design/intent of a percussion nipple and a vent hole liner used in the flintlock. Percussion nipples were designed to be “effectively” replaced with a securely-operable wrench. In addition to cleaning the excessive fouling with the revolver, a primary reason for easy nipple removal was that percussion nipples were made of softer iron based metals of the day and easily deformed/mushroomed, thus effecting placement of the cap. They were often replaced. Even the modern percussion revolvers and rifles with their superior metals should NEVER be dry fired for this reason….But, I have seen countless percussion firearms over the years with mushroomed nipples. The removable percussion nipple also aided cleaning of the more “fouling-prone” flash channels found in some of the percussion rifle designs.
The flintlocks flash channel is a shorter and more direct design, and, with proper cleaning procedures, be effectively cleaned without removal. The shallow screw slots and Allen wrench provisions in the flintlock flash liners have the potential to do more harm then good. These provisions for removal can compromise the strength and performance of the liner with incessant/frequent removal. The major failures of liners over the years that I have observed is not only faster flash hole erosion, but the eventual fracture of the reduced thickness of steel at the screw slot which crosses the flash hole. The stresses of removal/replacement doesn’t help. Additionally, if the screw slot is vertically oriented to the pan, it can direct priming powder and/or fouling down into the lock-works with various lock designs. Over the years I have converted most of my rifles to the White Lightning design liners, and have experienced high reliability with superb performance. Just some of my experiences.