The current research study aimed to explore the utility of selected problem-solving tools and techniques in root-cause analysis to demonstrate their practical application. An experimental research design adopting a positivist empirical approach with a deductive strategy was followed to assess the effectiveness of a combined (8D & Six Sigma) problem-solving approach in reducing a high defects rate of a mixer shower assembly line. A novel application of the 8D framework in combination with Six Sigma and other analytical tools was found highly effective in reducing the reject rate from 11.84% to 0.11%. Successful identification of the root cause led to the implementation of permanent corrective action ensuring a long-term stable assembly process. The research study provided a problem-solving framework that was found effective in resolving a complex problem and implementing long-term corrective action in an assembly production line. However, this framework can be used in other industries. The research study provides a solution to a high number of leak rejects in a subassembly where “O-seals” are used between mating parts. It also provides analytical tools that were found highly effective during the problem-solving process.