99 Explorer trans fliud leak

i have a 99 Explorer 4.0. Recently i noticed spots of transmission fluid in the driveway. I thought this was strange because i just had the trans rebuilt a little over a year ago. (warranty just ran out). The fluid is coming from between the motor and trans, through the spacer. My first thought was seal. My question is, if the seal is bad, would it leak all the time? Sometimes it dont leak or a week at a time, but when it does, its almost pouring out now.