You'd sure know if you hit something hard enough to crack it. Sounds to me like there was a flaw in the metal and when it got good and hot and bothered from your bush-hoggin' it just couldn't take it.

Now if you had a International Harvester Cub like me from the 1940's that would never have happened. They probably made their oil pans outta recycled armoured plate from WW II!

Have you tried searching for a Kubota chatroom?

Cheerily,
Charley Noble