Proper Oil Level
Make sure oil is level with filler opening. Because you can reach oil with your finger does not mean oil is at the proper level. One inch of oil level is about one gallon of oil.
Drain transmission while oil is warm. To drain oil remove the drain plug at the bottom of the case. Clean the drain plug before reinstalling.
Clean case around filler plug and remove the plug from side of the case. Fill transmission to the level of the filler opening. If the transmission has two filler openings, fill to level of both openings.
The exact amount of oil will depend on the transmission inclination and model. Do not overfill; this will cause oil to be forced out of the transmission.
When adding oil, types and brands of oil should not be mixed because of possible incompatibility.