E32 LAD shocks repair

Have had mine rebuilt. It is usually the bottom seals that go. You can buy the seals (2ea Q4112 417cm and 2ea 2-119 N1470-70) for about $.75 each) from Seal Company Enterprises Inc., 925 N. Meridian, Oklahoma City OK, 73107, 405 947-3307. The shop charged me 1.5 hours as they didn't need to remove shocks from car. Beats buying new ones which the lowest price I found was from Eurasian at $315 each*.
(*update in 2006 they cost about 470 $ at www.autohausaz.com)
The following is the procedure was from Kermit Achterman:

If the LAD struts are leaking at the top piston rod seal they can't be effectively repaired. If the leaks are in the valve assembly at bottom the repair is very easy. You do not have to remove the strut to do the repair. Bleed the pressure from the system using the bleed valve on the side of the leveling valve. Remove the large hex nut at the bottom of the valve on the side of the strut. This is the one with the small plastic plug in its center. I believe this takes a 32mm socket. (I had to put the socket in a lathe and reduce the OD for a distance back of about 3/16")
Remove the hex nut and the entire valve assembly comes with it - as well as about a pint of Pentosin oil.
Once the valve is out, remove the plastic plug and insert a 4mm hex key into the stem of the valve assembly to hold it, and remove the nut on the top. Carefully lift off all the springs, washers, and discs from the stem, keeping track of their order and position. You now have the base body with the stem it it. The stem is held in by a small stamped steel hat section which is staked into the body. This is very easy to snap out, even without grinding out any of the stakes. Once the hat section is out, pull out the stem and there is a 1/2" quad-ring seal and a teflon backup ring. The quad-ring seal is a metric size but a U.S. standard size -112 is within a couple of thousandths of the same size and works just as well. The replacement quad-ring should be Buna-N (nitrile) material. You may also want to replace the o-ring on the base body. This is a U.S. standard size -119. Also get this in Buna-N material.
Install the new quad-ring seal and snap the hat section back into place. Re-install all the springs, washers, and discs onto the stem and replace the retaining nut. When you disassemble this make note of the amount of stem projecting through the retaining nut and reinstall the nut to the same depth.
Install the assembly back into the strut and bleed the air from the system. If you have a Bently manual, the air bleed procedure is in there. 
This entire repair procedure is quite easy and will take you only a little over an hour.
Most of the LAD leaks that I have seen are in this quad-ring seal. The piston rod seals seem to last forever. Also the struts last a very very long time - except for these pesky, but easily repaired leaks.
Good luck!
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and another link for that

http://bmwe32.masscom.net/gavin/LAD_strut_rebuild.htm