I'm sure someone had this job done right, but I couldn't find it. So here is how I did it. Looking from the back of the mower, you will see a 6mm allen bolt facing down on the pump, it will be just fwd. of the axel remove this, a spring and a steel ball will come out as well. Drain it, rock the mower to get all the juice out. Install and refill, I used 5w-30, some say to use other, I don't think it really maters. Yes the pump fluid and the differential fluid are separate, use a 80-90 ish gear lube in that. Hope this helps, I'll try posting pics as well.
3-YT3600's, 2-YT 6800's, 1-YT6700 for parts.