Manual: In a manual transmission, the problem is not so much the fluid degradation, but rather fluid contamination. This contamination occurs over time as the synchronizers, bearings and gears in the transmission wear out. The resulting metal particles then float around in the lubricant.
A lot of mental illnesses can have a genetic component, yes (eg. depression, bipolar disorder, anxiety, antisocial personality disorder, etc.).
Mental illness refers to all of the diagnosable mental disorders and is characterized by abnormalities in thinking, feelings, or behaviors. Some of the most common types of mental illness include anxiety, depressive, behavioral, and substance-abuse disorders. There is no single cause for mental illness.