As an old vw driver, the trick to finding an oil leak is to clean the transmission and look the next time you use it. I'll rip open a big cardboard box and drive into it, then poke the heavy crud off with a screwdriver. Next a quick wipe witha towel and wire brush, then when some more screwdriver and a rag soaked in paint thinner/mineral spirits. Doesn't need to be spotless, but often witha big leak, the part of the transmission near the leak is the easiest to get clean. Let it dry, start it up and do a quick drive off the cardboard and throw it and the ten pounds of greasy dirt into the trash and check the transition. Oil leak might be obvious. If not mow the lawn then check again.