Their warranty, like most everybody else’s, is for the original purchaser with proof of purchase. It is a limited lifetime warranty. Wear and tear isn’t covered. From Bilsteins website:
“Many of our products have a limited lifetime warranty. This warranty does not cover wear and tear of the shock. Warranty returns of our products are required to go back through our distributors. If you believe the product to have a manufacturing defect, you will need to reach out to your original place of purchase to discuss your warranty options. Here is a link to our warranty information on our website for your review.
CLICK HERE for more Warranty Information.”
I’m not sure about rebuilding them.