1994 Johnson 90 Rust Issues

[Phlex1]

Hello, I have an amazingly reliable old johnson outboard that has never let me down. However, it does have an extremely rusty steering control arm & trim motor cover. I have treated these areas regularly with rust converter but am afraid that they are getting close to the point of failure. I have two questions, firstly will a trim tilt unit from an 80's model outboard fit in place on the existing unit? (Only ask as I can get a whole 80's unit quickly & cheaply). Second, has anyone ever seen a steering arm fail from rust? Thanks in advance, Steve

[boats.net]

If arm gets very thin it could break but surface rust wont cause any problems.