Same thing used to happen in my mums car. When i first got my P's I thought it would be fun to run the gutter and take it for a spin on an oval. After 5 minutes of fun and a lot of coolant spilling out, it turned out to be a leak in a connection on the front of the converter. Once i gave it a trashing im guessing the pressure got too much for it and caused it to just snap on the elbow coming straight out of the converter. Not a very happy dad when he came to the rescue (turned out the heater tap also had it and we had to bypass the gas and run the car on petrol for a few weeks.). all i can say is check for loose connections and don't let it get to the stage mum's did. Also if it does turn out be become a big problem, just get a whole new gas system installed. Find the right people and you could get it for around $200 with the $2000 rebate. Good luck.