Two problems related to transmission not engage have been reported for the 1999 Lexus RX300. The most recently reported issues are listed below.
My daughter was driving her 1999 Lexus Rx300 to work when, in heavy traffic, the transmission completely disengaged almost causing her to have an accident. Several cars almost hit her while she tried to navigate the car off the roadway to a safe place. Carried the car to the local Toyota dealer (there is no local Lexus dealer here) and was told the transmission would need to be replaced and the cost would be $3,700. There were no advanced indications the transmission was having problems it just suddenly quit working. This is a very dangerous scenario and we are blessed that our daughter was not involved in an accident due to the transmission failure.
My 1999 Lexus RX-300 automatic transmission failed to engage in higher gear and continued at 2nd gear. I have flushed the atf with original Toyota type 4 atf fluid every 30k miles. This vehicle has always been well-maintained regularly and driven under normal driving condition.