Ditto on Aaron's post. You will get hosed with hyd fluid if you dont drain it first. Makes it a lot less messy if you can drain and let stand for a couple days to get done dripping first. Screens clean easily with some spray parts cleaner or spray engine cleaner. IF there was moisture in the tranny as well you may have some hand lotion consistency stuff on the filter. I like to dump a gallon or so of diesel through the trans to rinse as much goo out as I can before putting the plug and new fluid in. Just leave the plug out and dump the fluid in the top. You could even put the plug in and rock the tractor back and forth by hand to swish it around in the pan before draining. Works pretty good, be suprised what you get out sometimes.
Every bit of flushing helps.
Nick