IF there is oil leaking near the manifold that is calling for a fire, so don't trust your vehicle, and check it often when you park it to make sure not too much oil has poured out. Rear main seal to what? When someone does a hear all the seals get replaced, is just good maintenance practice. Specially when most shops warranty their service for 5,000 or more miles//8,000 kilometer or more. When most stuff can go wrong like your gaskets leaking because the head was not honed to wear specs(rooky mistake), and created too much heat damaging the nearest gasket to the point of highest heat. He screwed up, that simple. Now he can say many things such as you rev the vehicle too high. Did not properly do maintenance, etc.... Just make sure you got something written on a paper saying how much it was going to cost you and most important the warranty for the service. If he/she does not want to correct it get a lawyer involve.