Each party shall endeavor to procure from its insurers waivers of subrogation with respect to claims against the other party under policies in which the other party is not a named insured, and shall promptly notify the other party in the event that any such waiver is unobtainable or is obtainable only upon payment of an additional premium. If such waiver is obtainable only upon payment of an additional premium, the other party shall have the right at its option to pay such additional premium.