Try cleaning off all the fluid you can from the suspected area, then start the tractor for about one minute to build hydro pressure. Shut off the tractor and carefully look to see where the leak is coming from.
You might also take a piece of cardboard and place it at different locations around the suspect area to see where the stream is coming from, and going to. Wear some heavy gloves and don't let any exposed skin get in the way of the stream.
Under full pressure, the hydro fluid could be injected into your skin, a dangerous proposition.
You don't say if this is a new filter, but perhaps it was cross threaded or the as has been said, the ring around the top has broken. It could also be that you have hit the filter and broken the mount.
If the tractor is under warranty, it is best to have your dealer take care of the problem.
John