Water and moisture can get between the vinyl and roof. That combination can cause the roof to rust over time. Run the palm of your hand over the vinyl to feel for lumps. Any lumps can potentially be rust blisters coming out. Every case is individual as to how bad the rust is, if present. I would guess that most cases can be repaired without replacing the roof section. Those would be extreme cases.
You can just replace the vinyl on a 1969 if you want. All the moulding can be removed from the windows. etc.
[This message has been edited by Silver69 (edited 11-19-2001).]