Before you send anything to Bilstein, look closely at the piston rod shaft wear. If the surface of the rod shows any visible scoring or heat related rainbow finish on the surface of the shaft/s, Bilstein will not rebuild what you have without replacing them, and they are not included in the price. The rebuild cost, including replacing the shaft/s is more than just buying new shocks or struts and having them revalved, if that's what your intention is.
I say this not only out of experience, but with Bilstein being busy with other things, the wait for an appointment to have them done at last check was 6 weeks. After waiting that long to have them tell you what I just typed above is a serious bummer.
Their reasoning is, the product that they return to you comes with a warranty. They will not return an item to you in "as is" condition. If a shock/strut comes in for a rebuild with visual wear on the shaft, they will not warrant it for obvious reasons.
Your parts can be leaking, be completely blown out. Thats fine. Worn shafts are a deal breaker, and almost any visible wear invokes this deal breaker.
