When does a Lexus RX300 need to have the shocks replaced?

The shock absorbers have no set time either mileage or age related at which they "must" be replaced. The life of shock absorbers depends totally on driving conditions and vehicle use. We have a lot of customers with RX300 and RX330s don't see any pattern of shock absorber failure. Shocks need to be replaced if they leak, are responsible for tire wear, or no longer dampen chassis travel when encountering road bumps and pot holes.

a simple old test will tell you, push down 2 to 3 times on each corner of the car it should not bounce back down after you let go, if it does it needs new shocks.