It's time to let it go. After 19 years any substantial effort at repair would be throwing good money after bad. I also had a 2000 RX300 AWD with 225,000+ miles and it got to the point where once or twice a year there would be a sensor failure, alternator failure, or some other issue that would result in a major repair expense. Spending $1,000 for a repair (and a LOT more if it's the actual engine) is just not cost effective. My 2013 RX350 is still much the same vehicle as was my 2000 RX300 only so much better. If you really like the RX then rest assured that if you buy a decent used RX it will continue to serve you just as your current model has only without the specter of likely imminent component failure. Whatever might be spent on a repair would be better spent towards a newer RX. Good luck.