Well reading your last sentence you may be on the wrong site ? 
The Disco 1 does pretty well for lack of rust in the important bits, whereas as Series, particularly a Station wagon, has a lot of bodywork structure that will be showing it's age. Some of it complex to repair. However given the choice I would be repairing a Series over a Disco', but that is my preference.
Less there mechanically/electrically so less to go wrong ...

The Disco 1 does pretty well for lack of rust in the important bits, whereas as Series, particularly a Station wagon, has a lot of bodywork structure that will be showing it's age. Some of it complex to repair. However given the choice I would be repairing a Series over a Disco', but that is my preference.
Less there mechanically/electrically so less to go wrong ...