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.).
Genetic disorders can be inherited, in which case people are born with them, even if they are not noticeable at first. Some disorders, however, are not inherited but develop spontaneously when disease-causing mutations * occur during cell division * .