One problem related to engine burning oil has been reported for the 1999 Lexus RX300. The most recently reported issues are listed below.
Our vehicle's oil consumption began to increase at approximately 90k miles. It would take at least a quart of oil every 700 miles or so. The check engine light also illuminated around 100k miles. Finally brought it to our Lexus dealership and told that we needed a new engine block and top end overhaul. The reason given was "oil sludge" due to lack of proper service. The service dept quoted us 8,000 dollars to do the repairs. Unfortunately we did not have the money so we are going to try and find a new engine on our own.