when to replace struts on a 99 maxima
same as you would with shocks. When your get bouncing. lean on the corners of the body, and put your weight into it. then release the body and see if it comes back to its normal position. If it bounces, or goes above normal before it comes back to level, its time to take it in and see about new struts.
Some like to look for front tire cupping if no other sympton is present.