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.).
Genetics (heredity): Someone may inherit a tendency to develop schizoaffective disorder from their parents. Brain structure and function: People with schizophrenia and mood disorders may have problems with brain circuits that manage mood and thinking.