Found a good visual aid for ' when to replace shock absorber '
 

Learned another new thing today.

Found this on a Lexus forum:

https://testing-public.carmd.com/Tsb/Download/91824/S-SB-0032-11

Took a while to find a direct link to the Lexus TSB .pdf

Probably if you see oil leaking out as the TSB shows, but there are other ways they can fail. The classic test is to bounce each corner of the car. The protruding bumpers on my 300D make that easy, jump off it with one foot. Those with the purty sissy Euro bumpers will have to push the body down with their hands. If the shock at that corner is good, the car should come up, go down may 1/4 as much and not appreciably up again. If it keeps bouncing like a rocking horse, the shock isn't doing its job. Another reason is if the shock squeaks and spraying silicone "garage door lubricant" on the shaft doesn't help.

Good points. I just got rid of the PO’s set of KYB shocks on my 300d. They didn’t leak. They passed the bumper bounce test. The car just didn’t recover that well from snappy turns and bumps. I always hated the KYB shocks on my SD. That car didn’t pass the bumper test.

Anyhow I was feeling flush with cash and ordered front and back Comfort Bilsteins. The car handles properly now.