from 1999 corolla to a 2004 camery then to a 2006 lexus gs 300 awd..I have come to one conclusion....totoya mades good cars, but very bad engine.
all their vicheles born oil.
Ihave had my gs for seven years now, and has 174000 km, and It has been burning oil since 96000km.
I have done everything that ther dealers have required, I have questioned lexus headquaters, but still no solution for my problem.
Though my research on all three of my vehicles as well as connecting with other owners and toyota specialty machines, have learned that most totoya and lexus model have that issue once you pass the 100000km mark
Good News! Lexus has issued a Customer Support Program Recall on this car. The recall is tagged for "Engine Misfire (Intermittently Runs Rough)". The root cause is blow-by and they do a provide a complete engine overhaul. My GS-300 had the same issue exactly as you mentioned. It burned 1 quart of oil every 3K miles. It never ran rough - but my check engine light was on. The rings were bad. Now that they have been replaced everything is fine. Hope this helps!