Need advice on through-hulls repair/replace

Finally! I'm scheduled to get the bottom painted on my Cal 28. Need some advice. She is being hauled and professionally bottom painted at the Oceanside CA Marine Center. I have no idea when she was hauled and painted the last time or when any of the the through hull fittings were installed. I'm concerned about them and need advice on what to look for and how to tell if they should be replaced. She had a flush toilet which I removed but the through hull and valve are still in place -- no leaks. What should I look for below the water line?? Should I seal off the head fitting or leave it for the eventual next owner? Anything I need to do with the hull, keel and rudder?? Thanks for any and all input.