what constitutes the need to replace

Are the forks or shock leaking oil or binding in the stroke? Have you taken the fork springs out/shock spring off and moved them through the stroke? I know you are trying to get off cheaply, but if you don't look inside, you will never know for sure. I think the best way to check the internal parts is to completely disassemble them, then clean and inspect them. I have taken apart one '87 KDX200 shock which had lost oil. The piston rubbed into the body, damaging both. The shaft chrome was worn off inside the body, out of sight. The seal head was damaged, too. The piston and valving assembly had some rust on it, too.