Vaillant boiler breaking down -- impossible to order replacement parts because of unique supplier

Last month, our Vaillant boiler started making strange airplane take-off noises from time to time. See: https://www.youtube.com/watch?v=yjyI8D03zII and: https://www.youtube.com/watch?v=EnOoDrUyHkc The local council was coming buy to do their periodic inspection and found the boiler's emissions were well within tolerances. They suggested we get an accredited chimney sweep also "SSIGA" certified to clean gas boilers, which I did, selecting one from the following list: https://m4.ti.ch/fileadmin/DT/temi/domande_costruzione/polizia_fuoco/Elenco_spazzacamini_08112017.pdf That gentleman came, opened the boiler and began performing his cleaning. While he was doing his cleaning, the heat exchanger coil broke, beginning to spurt water from the bottom left in the picture above. Time to call our trusted plumber. Our plumber looked at repairing this coil as a temporary fix, but was unable to because of the mix of metals used in the heat exchanger tube. No problem -- let's look...