When I got my Lexus last October with 76,000 on her she was using a lot of oil. I changed the oil when I got her, then at 78,000 then again at 83,000 and she hasn't used a drop in the last 500 miles so hopefully this has helped her. She had full service history but oil only changed every 10,000 or two or three years as car wasn't used a lot which is way too long between services.
This causes the piston rings to get gunged up and stick to the pistons. I used Castrol GTX oil for all my oil changes.