I had a Peugeot 504. Very comfortable car but very rusty. Engines were prone to condensation and even my dipstick rusted and eventually broke. Parts were a nightmare as they kept changing suppliers. The dealer told the chassis number was no use, bring the old part so he could identify it and he would see what he could do.
Anything from that era rusted, the French were probably the best at corrosion resistance, especially when compared to anything Japanese, German or Italian. There's a local farmer here who's collected several 205's, they've been sat outside in Welsh weather for several decades and still have barely any bodywork rust.