Per Countyline Lexus here in Hollywood, FL the factory warranty is 4/48
I bought my '01 GS300 6 weeks ago. I realized after buying it from a non-Lexus dealer that one of the rear shocks was bottoming-out. When I took it into the dealer it had 48,200 miles on it. I was prepared to pay to have the shocks replaced since it was actually outside the warranty. Without even asking, my service guy put everything through under the warranty and I didn't have to pay a penny.
So, if you only have 42k on yours, you should get it into the dealer, explain the problem and let them know that you want to get it solved before the car goes out of warranty. If they give you any flack that because it was originally sold in say February 2001, that it's beyond the 4 year mark, tell them you want to see in writing what determines the starting point of the 4 years. If they don't want to give in at first, usually if you lean on them a little, they will give in. If not, that's why there's the national customer service line.
BTW...this happened a couple years ago on my Acura. When I told the the dealer the tranny was acting funny, they did a complete service on it under warranty.
Hope this helps...