The tcase vent is in the tcase shifter/top cover plate. Little rubber mushroom. That's upper frontish. Been at any steep angles lately? Fill plug tight? If I 'member right, most of the sump tcase lube is in the chain housing, and the drain is in the bottom of the driven sprocket (output shaft case. Hard to get a leakable amount of lube to the top front of the case. The upper gears barely run in lube at all to keep the shaft drag low. Could the leak be at the tcase rear driveshaft front yoke seal. and be running "downhill" down the taper of the rear output shaft housing to the chain case and down it to the drip point? You crawl under and look. I'm too old and stiff right now.