Go spend some time on bobistheoilguy.com forums. These guys have motor oil running through their blood. They have some real experts there. Some are professional and some are just oil geeks but they get to the brass tacks on oil and lubrication issues.
The main thing is not to overheat the transmission. The life is inversely proportional to the oil temp. When fluid starts to turn brown as opposed to pink it is time to change it. Blackstone labs is a good place to get oil and fluid tested.
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