krava

I have an 06 gs 300 awd. I put 128,000 on it. I have done every service and oil change like I am suppose to do. I was in a rush to get to Dallas and had to take it to time it lube. After 1800 or so miles I had to put 4 quarts into it and it gave me a low oil warning before I did. Then I drove it another 3200 got the oil changed at the dealership. Now I have 2800 more miles on it and it didn't say low oil but I had them check it and they had to put another 2 quarts or so of oil in it. very seldom I can smell a faint smell of oil. 1.5 years ago I got new cams etc put into the car under warranty at 98,000 miles. Any suggestion as what I should do or is this normal? should I now put syntetic in it along with Restorer or some Lucas?