Faulty engine sump

I have a 2007 man truck TGA 26 480 today 5/2/2015 i saw what looked like oil dripping under my truck. I crawled under my truck and dipped my finger in the fluid and smelt it was motor oil fluid. I took my truck to my trusted mechanic and he pressed on the sump where the leak was coming from and informed me that the sump was warped in other words the sump wasn't sitting flush with engine and a gap had formed through the gasket. my question is how can this happen, has this happened before. I called m a n Australia which are located in Brisbane and they could not help me. I am not very happy because this is going to cost me $3,000 to fix. I would like a respond to my question please.