Clean and dry the transmission, go for a drive, then find the source of the leak. See if it's coming more from the front or the rear. Front could be the transmission cooler line (red plug in the picture), rear could be the black piston cover in the picture. The modulator can leak but that usually causes the vacuum pump to suck ATF through VCV and mess with shifts. Maybe it's an external only modulator leak. The modulator is the turret with a vacuum line fitting ahead of the shift lever.

Sixto
87 300D