Automatic Transmission Problem

[Nicutlass_Supremacy]

Recently when I start my car and put the gearshift in R position or D it seems that I´m in N position because the car doesn´t move. If this happens (because it doesn´t happen every time) I try another time changing gears and the car moves. I checked the automatic fluid because there´s a leakage within the gasket but it´s above the level, could this be the problem?. There´s a way to check the level? What I do is turn on the car and put all the gears then I turn of the car and check the level. Thanks!!!

[RobertISaar]

trans fluid needs to be checked with the engine running, preferably with the fluid warm/hot.