Mich. Comp. Laws § 445.834

Sec. 4. (1) Except as otherwise provided in subsection (2), the service dealer shall return all parts removed from the appliance to the customer unless the customer declines, in writing, to receive the removed part. (2) The service dealer may retain any part that has a core charge or exchange rate, contains hazardous material, or is returned to the manufacturer as required by the manufacturer's warranty if the service dealer provides to the customer, at the completion of the repair, service, or maintenance, a written statement on the final bill describing the reason for the retention of the part.