Sorry but I’m not sure I understand what you mean by this. Do you mean that there can be a coating of rust that can form on surfaces in the cooling system? If so I wouldn’t necessarily wanna dislodge that stuff and cause a blockage, but I’m not sure how much of a risk that is. Idk it seems like sometimes in rigs this old PM can do more harm than good like transmission flushes and the like.Personally, I don't view rust and deposits as being structural.