Rust In Radiator

[SKY 34]

hi,

I went servicing my car last week and the mechanics found that there are rusted stuff collected in the radiator.... the metal sleeve at the engine inlet from the radiator is rusted and cannot be replaced (Nissan don't sell the parts)...Rusted conenctions circled in attached picture.

The mechanics said that he flushed the system off rust already...

I am advised by friends that this problem is quite severe, he said that any part of the engine with the coolant running trhough may be rusted.. this include the engine itself... how true is this? the radiators are already replaced and a custom sleeve is waiting to be made and tested...are there no other solutions to this than to go for engine change?

Since I receive the car I have been chaning my coolants regularly, unfortunately previous Japanese owner did not take care of the car well