Add my congrats to your NEW old '98 ES 300 I also have a '98 ES 300, Pearl White which I bought two years ago with 65,000. Now has 135,00 and still runs great. Have little maintainence done except normal maintainence,(tires, oil change, brakes etc.) The only major repair was that I replaced my struts a couple of weeks ago which I think was an error on the mechanic's misdiagnoses. Put new tires on and had a poor ride above 70 MPH. After several re-balancing of the tires, mechanic recommended replacing the struts. Replaced them and had the same problem. (even created a new one) We found out that the tires were improperly balanced. Corrected the balance problem and the car rides like I'm on a cushion of air. Also corrected the problem with the new struts. Addressing your clunking in the front end, I also had that clunk and I was thinking all sorts of things as to the cause of the problem. Thanks to the Lexus Forum and their help, I found the cure. (This was before I replaced the struts) A few squirts of lubricant on the top of the struts mount, (enough to adiquately lub it and get the oil into the mount). Simple but a great fix. This is not saying that you might not have other problems with the suspension. This fixed mine. GOOD LUCK!! and enjoy your Lexus.
See my post on my strut replacement problem.