I had to change the upper control arms on my 2006 XJ8 and the right front shock fully extended and lost some oil (probably about 2 to 3 oz). I compressed the shock and reinstalled it. There is no air leak and the car rides fine but I would like to top off the shock oil to the correct amount and type of oil. The left shock didn't fully extend so there isn't a problem with it. I would just like to know why the right shock extended so far and why there was pressure still in the shock after I released the air pressure and took the air line off. When the shock extended, the residual air pressure still inside the shock blew the oil out the bottom.
Thanks,
Terry

 

You cannot add oil the air shock is a sealed unit

 

The air spring units are sent from the factory with air pressure in to prevent the unit from being moved before it is installed. This is to prevent rotation and damage to the diaphragm. So air pressure in the unit at all times is the norm and not unusual. However, oil seeping out of the unit indicates the seals are gone, so the unit is scrap. There are internal stops on these units that prevent over-extension even though they have air pressure; this is completely normal and not a fault; if the unit over-extended this indicates internal damage due, (maybe) to road-inflicted damage.

How many miles on this car, because this is the first post I've read about oil leaking out of an air spring ?

As Clifton94 says, you can't add oil. In fact I cannot think of any shock absorber where you can add oil; those days are long past. I think it might be prudent to replace that air spring unit; there are plenty on eBay, some used, some new. Check to see if it is Comfort (green spot on the label), or Sport, (a red spot on the label), because you do need the right one. You only need to replace the duff unit.