What I suggest is to clean up the area with degreaser the best you can and really try to isolate the leak. Snap a picture if you can, that way folks here can zero in on the issue.
In regards to this:
Is it bad to leave it in gear when parked?
Is it bad to pull it into neutral without clutching?
Leaving it in gear when parked is probably a good thing, especially if you live on a hill, that way your rig doesn't go rollin down the street. That should be fine, though sometimes on a large incline/decline you will get a little binding when parked. What I do is stop, press ebrake, THEN put into gear.
Regarding the neutral, I'm not super advanced as to the internals of this but I would use the clutch. When going through the gears or from gear to neutral.