The gas jet problem appears to me to be simply a case of a fractured copper pipe. Most model engineers should be able to perform a repair, probably by silver soldering a union or elbow at the point of fracture.
Copper pipe is usually quite malleable, maybe it had work hardened by repeated adjustment and may have been cracked which in turn might have caused a small gas leak and be the cause of the initial problem.
In my opinion the worst case scenario would involve obtaining a new burner and matching boiler as the 'firebox' is very much part of the burner design. You may even consider a new matching gas tank and regulator.
When I built the loco in my avatar I used Roundhouse bodywork, motion, frames and cylinders with a custom built boiler, burner, gas tank and regulator from Tony Sant of Finescale Engineering. Tony's system has performed faultlessly for nigh on ten years but he may have retired by now, however I notice in the link to Chuffed 2 bits in a previous post that they are agents for Finescale. Based on this I suggest one option would be to approach them with your problem if you can't get it sorted locally.
