Just fitted an add-on third octave key and accessory left hand F# key to an older oboe. Good silver to silver welding practice. I use silver filler rod and silver soldering paste from Rio Grand jewelry supply. They also sell a brass and bronze filler paste that works ‘ok’ but I have not decided if I’m just having a skill issue. I have several hours of polish work left. I‘ll get back to the Yarrow boiler once I finish. I’m deciding if I need to swedge the 20 tubes in the upper and lower barrels.