I noticed the mower started to move a bit slow, but didnt think much of it, and maybe a 60-90 seconds later smelled something, so I turned back and saw oil all over the platform the engine sits on, and smoke rising from the engine. So, I shit it off abruptly. I didn't even turn off the blades. It backfired pretty loud.
I went inside and let it cool down, and came back out about 2hr later. The oil was completely drained. The oil was fine before I started, I figured filled it back up figuring I could at least drive it to the backyard to work on it. The engine shut off within 2-3 seconds, but I didnt hear anything particularly loud then.
That's when I discovered the crack. Obviously, at that point the oil drained out again.
I'm not sure if I could have missed the sound of the engine cracking the second time, but idk how loud that would really be. So, I'm not sure when the damage was done. I did find a spot that was barely connected that might have been when it leaked out the first time, or it might have come loose when the engine blew. I'll post some pictures when it's light out tomorrow.
I'll also call the place I got the mower from tomorrow and figure out how long they had it. Mu first guess when I saw the leak was that a gasket or something could have dried out if it sat unused for awhile, and that seal just failed when I was riding it.