Good to hear you got it fixed..... I hope they did not charge you much as that is a piece of cake with a tig welder. A wire welder could have worked also, but when tig welding through a rosette hole one can be 100% sure that the shaft gets melted/penetrated prior to dipping in the filler rod thus melting/mixing it together with the outer sleeve. I use rosette welds all the time when internally splicing chrome moly aircraft tubing.
While some of the other ideas would have worked, five years from now Seahawk won't have to explain to his wife why his heat system just started acting up in his silly old German toy car as they are on a fall color tour two hours from home.
Keep up the good work Denis... don't let Seahawk rush you... quality resto work like you are doing takes time.