What is the average live of those ones in a X5?
There is a recommended time to change them? (They are quite expensive in Europe)

__________________
BMW X5 3.0i e53 (2000)
Mazda MX5 1.8 Unplugged NB2.5 (2004)
Skoda Octavia 1.6 MPI GLP-Etanol-Gasolina 1Z5 (2009)
Audi A4 1.9TDI QUATTRO ATJ (2000)
Peugeot 306 GTI-6 2.0 (1998)
Yamaha XJR 1300 (2000)