This document summarizes a systematic literature review on maintainability challenges in machine learning systems. It identifies challenges at different stages of the ML workflow: data engineering (messy data, lack of transparency), model engineering (hyperparameters affect performance and testing is difficult), and building overall ML systems (lack of common programming models, need for expert intervention, and "pipeline jungles" due to connecting various components). The stages are interdependent, and qualities like data-dependence, drift over time, and bias handling must be addressed for a quality ML system. Implications include the need for standard tools for provenance, publishing models, querying transformations, and infrastructure for deployment and maintenance.