my 1993 SC300 has almost 85,000 miles on it. on average when is it time to replace the shocks?

 

If they're still good why replacing them, unless you want to try aftermarket shocks?
I've seen several people with leaking shock (1) at 50-60K, myself included.

 

Stock shocks really don't last more than 20,000 or so. You just wouldn't notice unless you replaced them.

If you change them you will notice a significant improvement in ride quality and handling.

Todd M.
TM Engineering
http://www.tmengineering.net