Isofix was fitted around 03/04 I believe, not seen any sf's with it bit I know the sg's had it, Mr b will be best person to ask,
The sls is a pain in the !Removed! literally, Easiest way to check the car is still OK is visually, if it looks like a dog squatting on level ground it's not good, alternatively of you go view any foz, stick your hand on the rear arch lip and lift it up if it falls back and sags loads then the suspension is shot.
Not a big issue if it's knackered, pedders do bolt in standard shocks and springs that bolt straight up, and you can get custom spring and kyb shocks for same price,
If you see a car that you like and it looks saggy knock 300 quid off the price, if they refuse walk away !
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