Used Kegs, hardware questions

I just purchased two used kegs with remnants of soda in them. I'll be the first introduce them to home brew and this is also my first run at kegging.

To clean the outside I have plenty of goo-gone and bar keepers friend, but what about the posts, poppets and relief valves. I know the seals need replaced but how do I know if the hardware itself needs replace? I'd hate to find out they need replaced when I have a full keg of brew.

Both are Ball Lock, one is a corny the other is firestone.

You probably won't have to replace any hardware - I have a dozen and none of them required more than seals. Check to see if the kegs hold pressure. I have replaced the seals and poppets along the way, but the posts have been fine.