Final answer:
The most suitable tool for identifying multiple sources of quality decline in automobile parts is a Fishbone (Ishikawa) diagram, which assists in root cause analysis and involves gathering information from stakeholders.
Step-by-step explanation:
When an automobile parts manufacturer is faced with complaints from customers about declining quality and the problem seems to have multiple sources, the most appropriate tool for performing a thorough problem identification process is a Fishbone (Ishikawa) diagram. This diagram helps in doing a root cause analysis to identify the underlying issues behind the perceived drop in quality. It visually represents multiple potential causes of a problem, which can then be investigated individually.
A Fishbone diagram is particularly well-suited for situations where there is a need for gathering information from customers and other stakeholders to analyze and categorize potential contributing factors to the quality issues.
Other tools mentioned, such as a Pareto diagram, histogram, and ISO 9000 audit, have their own applications. A Pareto diagram, which organizes issues by their frequency and shows which defects are most common, could also be helpful after the most significant causes of quality problems have been identified using the Fishbone diagram. A histogram may be used to look at the distribution of data but is less effective in identifying root causes.
An ISO 9000 audit is a formal review of a company's quality management system, not a tool specifically designed for identifying the causes of a single problem.