I've been facing same problem for over a year now. Bought IS 250 2008 and it already had very less (shouldn't have bought it in first place). After logbook service at 107000 kms, noticed significant oil dropping, as car gave oil warning and knocking sound. I topped up oil with 5w-30 and then took it to mechanic. They checked, no leakage no blue smoke, i checked where I parked no signs of stains.
Anyways, they topped up oil, added thickener. Then again after few months I noticed oil dropped to minimum. Topped it with 5w-40 (only oil I could nearby). And again same problem, oil is low. I am aware of carbon build up but this is too much. Has anyone got piston rings replaced?
Whats the permanent solution? I don't think my mechanic is capable of handling such issue.