1999 Cougar Oil Overfill

I have a 1999 Mercury Cougar V6 2.5L Duratec with 49K milage, I'm the original owner with good records of maintenance/oil changes, last oil change I noticed Oil level at least 1/2 inch above MAX on diptstick while cold and sitting over night. I called the car shop that did oil change, they said bring it in. Drove 15 minutes to shop and when they dipped the stick it showed Oil right at MAX right after engine shut off. I explained to manager that oil was 1/2 inch above but he assured me that car was safe to drive even though I explained car manual warnings of above MAX could damage engine. I believed his judgement and drove 1200 mile round trip to desert and back home. A few weeks later I smelled burning oil on manifold. I took car to shop and manager, he examined underside and showed me where oil was leaking on both front and rear areas of engine. He was adamant that his shop was not responsible for engine damage and that his shop had not overfilled the engine with too much oil. What are chances of both front and rear seals leaking on their own and chances of damage after suspect oil change? The Owner Manual is very specific about nothing above MAX level. Any thoughts? What other damage should I be concerned about? Thanks guys. In desperate mood here!