Dometic says in their owners manual to never allow the foot lever to slam closed, to close it slowly or the mechanism will break.
I rebuilt ours and the new spring pack was much weaker than the original, perhaps related?
I was going to say... No, I didn't replace anything but the ball drive arm and valve. The breakage happened, I'm sure, because we were purposefully slamming the foot lever closed.
But yea, the reason was a poor seal of the ball at the gasket inside the bowl. The ball wasn't moving fully to closed position. OK, so perhaps it is because of an
original weak-ish spring, but now that it's back together, it's holding water just fine. I'm thinking the gasket rim may need to be lubed occasionally with silicone so the ball slides smoothly into place. (?) Maybe it shouldn't have to be. I guess I'll see if the problem comes back.