Here you can kind of see how all those things come together. Dan is assembling the ATS-custom "hydro-balanced spring and sleeve." The idea is to provide a smoother and more-controlled fluid flow through the transmission for more precise up-and downshifts. ATS also modifies it so that there is oil flow through the transmission when it is in park. The stock configuration only allows flow in neutral and in gear, which can lead to heat build up if you are in park for extended periods.