Air Lift Suspension on 4.4is??

[we350z]

Hi guys - my X5 is at the shop getting checked out for the "SELF LEVEL SUSP INACT." code that has been persisting for the last month or so. Here is the thread regarding that:

http://www.xoutpost.com/bmw-sav-foru...g-rh-side.html

So they are saying the driver side has a leak, which is no surprise to me it's been like that ever since I bought the car from my dad 7 years ago. It's a slow leak so if the car sits for a couple days it will sag. Upon starting the car the compressor always pumps it right back up. It still does this, but now the module is reading a fault consistently. Perhaps the leak has gotten worse...

This is the diagnosis the local shop (Holland Auto Care in San Mateo) is giving. They are quoting $740 parts and labor to replace just the driver side bag and there is no guarantee that will resolve the issue (though it likely will). They may need to continue troubleshooting at additional cost. For that kind of money I would much rather covert to a traditional coilover system in the rear or go big and spend the money on an adjustable air ride system like this AIR LIFT 77786 (even looks like there is a promo for $50 off!):

Air Lift® 77786 - Performance Air Suspension Manual Slam Combo Kit

The shop here won't install anything aftermarket so I'll have to take it to another shop, preferable a race shop (probably Rennsport in Reno, NV).

What parts would I need for the rear if I wanted to just do shocks and springs? I definitely want to lower the truck if I go this route since I love the look though it would be great to have the best of both worlds...