There are two types of rear unit, Comfort (Green Dot) and Sport (Red Dot). However the Dot is difficult to see sometimes at the top of the unit. If you see the Part Number (F308609101/f/02) on the Air Suspension Unit its a Green Dot.
Also, my replacement came from Auto Reserve in Derbyshire. They seem good for used parts.

 

I have F308609101/F/02 on my rear suspension strut yet most of the struts for sale seem to have a different format - such as C2C31014 there seem to be lots of different codes depending on vin number and whether sport or comfort. I can understand the sport or comfort difference but are the later VIN number ranges just the same item but maybe improved such that I could fit the later ones without any problem. I am also surprised that in some lists that check the right model, a 2003 xj8 4.2 has compatibility for a certain strut, but a 2003 xj8 3.6 is not compatible. I would have expected the rear suspensions to be identical. Can anyone unravel the mystery of all these codes and types?