It is important to promote the reuse of products in order to create a circulating society. For this purpose, the management of products and parts is necessary not only at their manufacturing stage but also throughout their entire life cycle, including use, collection, and disposal. To achieve this, we are developing a part agent system. The part agent system assigns a dedicated network agent to each product and part. The agent moves on the network, following the corresponding product or part in the real world. It retains and collects information on the product or part, including the lifecycle, manufacturing information, current status, and operation history. Based on the information, the part agent advises the user in making decisions regarding the maintenance of the product or part. In this study, we focus on the workload of the module as a value related to the deterioration and environmental load of the module. The part agent monitors the workload of the corresponding module, determines the appropriate replacement of the module based on communication and negotiation with other part agents, and generates advice to the user on the replacement. In this paper, we describe a scheme applied to a modularized manipulator, propose a method for a part agent to replace modules based on the joint workload of the manipulator, show some early simulation results, and discuss the issues with the method.