Do these require adding oil to the strut housing ?
I cant remember where i read this, and just looked for it again without luck..
If it's an Bilstein Upside down construction it's my understanding that it's recomended against adding oil to the strut housing, as the shock seals are contained inside the strut, and the oil could damage the rubber in those seals.
The upsidedown construction can be considered like an ordinary shock except that it's the bottom that sticks out , usually this is very thick to acomodate the valving. And the strut is sealed with a large screw with a rubberseal.
In other words, the piston is fixed inside the strut, and the cylinder is what moves in relation to the piston.
Where on a standard design its the other way around.
Hope to help..