First of all, periodically, it's necessary to perform transmission fluid maintenance. Acquire the required transmission fluid and a new filter. Raise and support the vehicle on jack stands. For 42RLE and NAG1 transmissions, remove the front and side transmission pan mounting bolts with a drain pan underneath, and loosen the rear pan bolts. Also, carefully pry the transmission pan loose to allow the fluid to drain. Remove the remaining bolts, pan, and gasket, cleaning the transmission's gasket surface thoroughly. Drain the fluid from the transmission pan, clean it with solvent, and remove the filter and seal. Install a new filter seal, then the new filter, and ensure the gasket surface on the pan is clean. Install a new gasket for NAG1 transmissions, apply ATF-resistant RTV sealant for 42LE transmissions, and tighten the pan bolts in sequence. 42RLE and NAG1 transmissions require a dipstick and a scan tool to read the fluid temperature.