Engine Cooling System problems of the 2004 Infiniti FX35

I started my car up on the morning of 6/1/12 and I notice it was shaking. I drove it around the corner and shaking got worst and the engine light came on. I parked the car. Called infinity discussed problem and brought the car in for service the sameday. Today I get a call from the services dept and I was told I need a new engine. I was told the problem was miss fire and oil build up, and it was unrepairable. And I should have gotten more frequent oil changes. In 2011 the engine light came on my car was reported that is was my cooling system. It was repaired. Nothing was reported that is was a problem with the engine. I faxed the services dept records from sears of oil changes. I went to several other places since 2004. But I have no record.