Thanks, no previous owner, just me trusting blindly the mechanic, and specially last pandemic year mostly standing outside with almost no use... I have decided to take care of it myself from now on...
Learned the hard way, and now with new downpipes, rebuilt all coolant pipes, silicone hoses, new pressure clips, all new set of O-rings prepared to fit (even thermostat, that may be needing a new housing...), and specially a roof to give the bike some shelter, I am in the hope of at least a few years more without incidents...
On the barrel adaptor (solidified to the almost died metal pipe, that may be requiring some work soon), I used some limescale remover (but made mistake of submerging into soapy warm water, and lost finish), and was able to remove all of it, but I don't see how to do it on the barrels without risking barrel flat finish (if using sharp tool), or final cleanup (if using some product). I can always find a second hand adaptor, but I don't see me changing barrels...
Question was more about what to do with it, to fit the adapter directly with new O-rings properly greased, or try to do something about it, I reckon that it will always be better than it was even if left as it is right now...
Thanks a lot for the response,