I'm not familiar with the construction of flybacks in European TVs, but your chassis does not look severely corroded, overall. I have seen radio and TV chassis with more surface rust than that, and their transformers were not harmed. Outer appearance is not necessarily a good indicator of a component's internal health. A dedicated flyback tester can check the flyback electronically. I don't know of an easy way to judge whether it might have absorbed too much moisture.
If you don't have a huge oven, you could place a flood lamp near that part of the chassis and let it warm things for a long time (say, a couple of days). Better than nothing, and it might help.
I like the appearance of your TV. Vintage European televisions are never seen here (on the West coast of the US), so anything of that nature looks exotic to me.
Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html