Say, if I could trouble you further..
Can you give me a rough estimate of how many transmissions you repaired in a given year and the aproximate population of the city or town you were located in? Did you ever try to arrive at an average of when they failed exactly?
I really wanted to specialize here. Deal specifically with transmissions. It would cut down on the parts inventory and specialized equipment significantly.
I honestly don't have much interest in being a catch all mechanic.