I am sure that the Service Manager was using the Factory ATF, and by that, I would keep on using the Factory ATF. It is possible that changing to synthetic at that point would cause more problems.
There are a few pretty comon spots for those transmissions to leak, and after that kind of mileage, I would expect some leakage. I woudn't worry about it too much, but it would be a good idea to find out what is leaking, that way you know. And if it is something small, then I would get it fixed. If it is anything big, I would just let it go and not worry about it until it gets worse.