I have a 1960 Electra. I got it with 42,000 original miles a year ago. I've put 5,000 miles on it since (I love the car). The motor is powerful, uses no oil, runs cool & starts at the slightest provication of the starter. Lately I'vre noticed some tapit noise has developed, not terrible, but not there before. When I got the car the oil was clean, but I've changed it 3 times since, using Castrol 10W30. What might this be? What oil and/or additive can I run to keep her quiet? Dan