Looks like its a gearbox out job to find the source of the leak, most probably the output shaft oil seal leaking and finding its way to the joint you circled.
2 litre parts diagram here for info but check Realoem site using last seven of your cars vin number for correct diagram
BMW parts Z3 E36 Z3 2.0 S5D...G housing + mounting parts
www.realoem.com