Engine problems of the 2005 Subaru Forester

My 2005 Subaru Forester, has been serviced regularly at dwyer and sons Subaru dealership in commerce, michigan. During all scheduled maintenance, I've always discussed with their service department that I have a potential problem with the engine. The engine would downshift very hard or seemed like something was "banging. " or running very rough. The rpm would also seem to run lower than normal. Every time I made them aware of the problem, while the vehicle was under warranty, the dealership was never able to diagnose the problem. So, every time I brought the car in thereafter, I told them to make note of the issue and that it hasn't gone away. Again, they would road test the car and always state that they found nothing wrong. Now, the vehicle is just out of warranty and the dealership stated they found the problem. This problem would require an entire engine rebuild on a engine that is meticulously taken care of and only has 75,000 miles on it. This repair they were just able to diagnose is going to cost $5,900. They indicated the dealership would only pay $1,500 toward the repair. I told them I am not responsible for this, especially since they've acknowledged the problem existed before and I made them aware multiple times. This engine problem had pre-existed right from the factory, and their are potentially other Subaru Foresters with the same problem. I should not be held financially responsible for this engine repair and feel Subaru should be held accountable for allowing this vehicle to be sold and be responsible for the repair or, a new engine all together.