I would definatly take them to court and sue them. The gumout is strictly a detergent and provides very little lubrication. Try to find a bottle of the stuff they used and see what the directions say. I'm sure it says drain only a quart of oil and replace that drained quart with the cleaner. As far as your motor goes, it sounds like its totally destroyed. With no lubrication, the rod bearings are going to be ruined. I'm sure other parts of the engine have suffered damage as well. If they used the product improperly, you'll have no problem winning a court case and getting them to pay for a new engine. Good luck!!