Engine problems of the 2003 Lexus RX300

While traveling out to denver from omaha, received low oil pressure light on my 2003 Lexus Rx300. Pulled over immediately, had car towed to Lexus dealership. They immediately knew what to look for and say. . The car has been misused, (no oil changes) and oil gelling was result. Within minutes they said the engine was shot and would require new engine. They showed me the sludge which was only found on one cylinder head, by the oil return line. Quantity was about one handful and as stated, only near the return line, remainder of head clean. I had changed oil night before trip. They will not honor power train warranty, since I cannot prove oil was changed every 7500 miles. Car has 50,000, and I purchased car from individual who stated he always maintained car but cannot prove with receipts. Called customer satisfaction line who said unless I prove the original owner had oil changed they would not honor. Dealership had stated today that only one head is damaged, the other is fine. Short block will require replacement as well. If it was an oil change issue wouldn't the sludge be in both heads and why was the sludge only found in one small section of head, by oil return line. If this were a lack of maintenance, sludge should be everywhere (both heads) not just one area. . . Lexus stated it is my fault and they do not have a design issue with this v-6 although I have never seen oil gel like this. . . Regardless of maintenance history. Lexus reputation is big joke if their engines can't make it 50,000 miles.