generally when the tranny leaks in that given area, the main cause of the leak is the part underneath that area you described above. The is a small donut looking thing (can't remember what it's called) that is underneat that cover that you described above, where the tranny meets the drive line. Replace it and usually the tranny will stop leaking. Had this happen to several of mine. Cost of the part new is @$75.00. hopefully this helps.. it's worth a try