Again a purchase recommendation (S80 TDI)

Hello guys, a colleague of mine would like to buy it:http://www.brauchtwagen.at/detailansicht.php?id_fahrzeug=1778507 What do you think? Is the Audi TDI recommended? What do we have to pay attention to when visiting/testing? When to change the ZR? Are there known weaknesses? Thank you already!!! LG, Nordisk.