Roll it in flour and look for the wet spot?First, determine EXACTLY where it's leaking! Drain plug could be loose, o-ring could be bad, or bolts could be loose. If bolts are all tight, you'll have to drain trans. If a leak at the joint between the lower case and main housing, a sealant probably won't setup with oil in trans...oil will seep out, soften sealant and prevent it from "sealing".
Wash trans down with soapy water or parts cleaner. Wait for leak to show up so you know what/where your issue is. Bob