The mechanic has informed me that it will cost over $500 to have just the front done and between $700 and $800 for all four wheels. The rear uses what appear to be regular shocks that are mounted under the rear seat. The front has some cartridge system but there isn't any spring visible unlike my 1990 740 which has a fat coil spring around the cartridge. It also looks like the brake caliper will have to come off to access two big bolts . The absence of a spring is kind of puzzling.