Sad fact is... its a Ford - it will rust.
The mk1 Focus is been around awhile now (14years iirc) and even the RS' are knocking 10years old now. couple that with our damp climate, salted roads & Ford not being the best for underbody treatment and its a recipe for a rusty car.
Im not saying its only Fords that rust, nor im I saying they will all be bad. But its is worth a nosey and a poke around if you have one or are looking to buy one.