ZF5 leaking oil, can't locate the leak

[crazy_canadian]

My transmission is leaking a bit of oil, not much. I'd say a quart every 3 months or so. But it annoys me since my driveway is brand new at home.
It seems the leak is coming from the top, but I can't really tell because everytime I clean the casing, when I check back, oil is everywhere.

Do these trans has a common seal problem?
The truck has a little bit over 500k km on it right now.

[kanuck15]

This is a tad labor intensive BUT pull up the carpeting and pull the trans cover plate as well as the shifter. Sounds like the shifter plate area is leaking. A view from the top may help