Aardvarc Racing offers used Bilstein strut inserts and shocks for a variety of models, as listed below in the table. As you may know, Bilsteins are considered by many to be the best shocks available for BMWs.  They improve the handling tremendously while lasting for a very long time.  Fortunately, Bilsteins generally either work at or very close to the factory specifications, or they don't really work at all. This makes testing used units fairly easy. Therefore, used Bilsteins are considered by many to be a good bet, especially when you consider the cost of new set of two is about $200.  All Bilstein shocks sold by Aardvarc Racing are in good condition, come with the correct hardware, gland nuts, and dust boots, and come with a 90-day guarantee.