Just sent the inquiry to bike-breakers. Thanks.
Regarding the corrosion, the bike has been serviced by many mechanics for the past 15 years, I was relying on them so I didn't check if they all poured in antifreeze. I thought it's just a normal thing to do. :/
My current mechanic showed me the pipes, they are eaten from the inside, and T-pipe also broke so he had to weld it. Inside the pipes there was brown dirt that they had to clean, grease the tubes, change the clamps and pour in fresh antifreeze, but it looks like it didn't help, it still leaks