The local Subaru dealership replaced the leaking.

The local Subaru dealership replaced the leaking head gaskets 2000 miles ago. Subaru fixed it because this has became an issue with the 2.5i engine. O.K. The car was running poorly again I took it to the dealership for an oil change and they said the car was out of oil! The oil light did come on right before I pulled in. First of all when they did the head gaskets it wasn't due for an oil change. However it seems totally weird that it ran out of oil 2000 miles after the head gasket job. You would have thought they would have checked doing such a major job and made sure it did not leave the shop short of oil. They wanted to tear the engine down at my cost and then make up their mind on whether subaru would fix it. I asked them to put oil in it. I picked it up and there was a very slight knock, not all the time but on accelerating. However, I added STP and there is no abnormal noise. I just started it cold and there was no tapping etc. I think the dealership failed to make sure any oil that came out of the car went back in It doesn't burn oil, I have always had the oil changed regularly using synthetic. What are your thoughts?