T case Leak?

It looks like I have a bad seal on the front output of my Tcase. It’s leaking fairly badly. Is this prone to failure or should I be looking for a root cause? I have wheeled it a lot this summer. Also, what is involved in replacing it? Do I need any special tools?

The front seal comes out without too much trouble once you get the driveline and yoke bolt out (air tool). Get a hold of the lip, it might/should have some RTV on it but it'll come out.

So it’s just a pull the old one out, and press the new one in straight operation. Sounds simple.
I’m really wondering what caused it to go bad so suddenly. I have a 231 and a lockrite in the front so it is turning all the time, but that doesn’t seam like it would make it just start leaking like this. This is a bad leak that happened all at once.